From 69a3ed6939452ee4e466be7531f950e94b163fb1 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Nicol=C3=A1s=20Pe=C3=B1a=20Moreno?= <npm@chromium.org>
Date: Thu, 23 Jan 2020 22:57:12 +0000
Subject: [PATCH] Bug 1610669 [wpt PR 21326] - Use assert_precondition in
 ElementTiming/LargestContentfulPaint, a=testonly
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

Automatic update from web-platform-tests
Use assert_precondition in ElementTiming/LargestContentfulPaint

This CL replaces assert_unreached for assert_precondition for the API
existence checks in the ElementTiming and LargestContentfulPaint WPTs.

Change-Id: Icd2ff3e045835cf4c46a370a384455143a717308
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2013863
Reviewed-by: Tom McKee <tommckee@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734494}

--

wpt-commits: bd2c0495a860571b7467989e89dd51ebad4f9562
wpt-pr: 21326
---
 .../tests/element-timing/background-image-data-uri.html           | 4 +---
 .../tests/element-timing/background-image-multiple-elements.html  | 4 +---
 .../tests/element-timing/background-image-stretched.html          | 4 +---
 .../web-platform/tests/element-timing/buffer-before-onload.html   | 4 +---
 testing/web-platform/tests/element-timing/buffered-flag.html      | 4 +---
 .../tests/element-timing/cross-origin-element.sub.html            | 4 +---
 .../tests/element-timing/cross-origin-iframe-element.sub.html     | 4 +---
 testing/web-platform/tests/element-timing/css-generated-text.html | 4 +---
 testing/web-platform/tests/element-timing/disconnect-image.html   | 4 +---
 .../tests/element-timing/element-only-when-fully-active.html      | 3 +++
 .../tests/element-timing/first-letter-background.html             | 4 +---
 .../web-platform/tests/element-timing/fixed-id-identifier.html    | 4 +---
 testing/web-platform/tests/element-timing/image-TAO.sub.html      | 4 +---
 testing/web-platform/tests/element-timing/image-carousel.html     | 4 +---
 testing/web-platform/tests/element-timing/image-clipped-svg.html  | 4 +---
 testing/web-platform/tests/element-timing/image-data-uri.html     | 4 +---
 testing/web-platform/tests/element-timing/image-not-added.html    | 4 +---
 .../tests/element-timing/image-not-fully-visible.html             | 4 +---
 testing/web-platform/tests/element-timing/image-rect-iframe.html  | 4 +---
 testing/web-platform/tests/element-timing/image-src-change.html   | 4 +---
 .../web-platform/tests/element-timing/image-with-css-scale.html   | 4 +---
 .../web-platform/tests/element-timing/image-with-rotation.html    | 4 +---
 .../tests/element-timing/images-repeated-resource.html            | 4 +---
 testing/web-platform/tests/element-timing/invisible-images.html   | 4 +---
 .../tests/element-timing/multiple-background-images.html          | 4 +---
 .../tests/element-timing/observe-background-image.html            | 4 +---
 .../web-platform/tests/element-timing/observe-child-element.html  | 4 +---
 .../web-platform/tests/element-timing/observe-elementtiming.html  | 4 +---
 .../tests/element-timing/observe-empty-attribute.html             | 4 +---
 .../tests/element-timing/observe-multiple-images.html             | 4 +---
 .../web-platform/tests/element-timing/observe-shadow-image.html   | 4 +---
 .../web-platform/tests/element-timing/observe-shadow-text.html    | 4 +---
 testing/web-platform/tests/element-timing/observe-svg-image.html  | 4 +---
 testing/web-platform/tests/element-timing/observe-text.html       | 4 +---
 .../web-platform/tests/element-timing/observe-video-poster.html   | 4 +---
 .../tests/element-timing/progressively-loaded-image.html          | 4 +---
 testing/web-platform/tests/element-timing/rectangular-image.html  | 4 +---
 testing/web-platform/tests/element-timing/redirects-tao-star.html | 4 +---
 testing/web-platform/tests/element-timing/retrievability.html     | 4 +---
 testing/web-platform/tests/element-timing/scroll-to-text.html     | 4 +---
 .../tests/element-timing/text-with-display-style.html             | 4 +---
 testing/web-platform/tests/element-timing/toJSON.html             | 4 +---
 .../tests/largest-contentful-paint/contracted-image.html          | 4 +---
 .../tests/largest-contentful-paint/cross-origin-image.sub.html    | 4 +---
 .../tests/largest-contentful-paint/expanded-image.html            | 4 +---
 .../tests/largest-contentful-paint/first-letter-background.html   | 4 +---
 .../largest-contentful-paint/first-paint-equals-lcp-text.html     | 8 ++------
 .../largest-contentful-paint/iframe-content-not-observed.html     | 4 +---
 .../tests/largest-contentful-paint/image-src-change.html          | 4 +---
 .../tests/largest-contentful-paint/invisible-images.html          | 4 +---
 .../web-platform/tests/largest-contentful-paint/larger-image.html | 4 +---
 .../web-platform/tests/largest-contentful-paint/larger-text.html  | 4 +---
 .../largest-contentful-paint/loadTime-after-appendChild.html      | 4 +---
 .../largest-contentful-paint/observe-after-untrusted-scroll.html  | 4 +---
 .../tests/largest-contentful-paint/observe-image.html             | 4 +---
 .../web-platform/tests/largest-contentful-paint/observe-text.html | 4 +---
 .../tests/largest-contentful-paint/repeated-image.html            | 4 +---
 .../tests/largest-contentful-paint/text-with-display-style.html   | 4 +---
 testing/web-platform/tests/largest-contentful-paint/toJSON.html   | 4 +---
 .../web-platform/tests/largest-contentful-paint/video-poster.html | 4 +---
 60 files changed, 63 insertions(+), 180 deletions(-)

diff --git a/testing/web-platform/tests/element-timing/background-image-data-uri.html b/testing/web-platform/tests/element-timing/background-image-data-uri.html
index 3cac0f56db86..540668ae3c3b 100644
--- a/testing/web-platform/tests/element-timing/background-image-data-uri.html
+++ b/testing/web-platform/tests/element-timing/background-image-data-uri.html
@@ -18,9 +18,7 @@ body {
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/background-image-multiple-elements.html b/testing/web-platform/tests/element-timing/background-image-multiple-elements.html
index 44755d49f5c3..61a284a5df38 100644
--- a/testing/web-platform/tests/element-timing/background-image-multiple-elements.html
+++ b/testing/web-platform/tests/element-timing/background-image-multiple-elements.html
@@ -23,9 +23,7 @@ body {
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     let beforeRender = performance.now();
     let numObservedElements = 0;
     let observedDiv1 = false;
diff --git a/testing/web-platform/tests/element-timing/background-image-stretched.html b/testing/web-platform/tests/element-timing/background-image-stretched.html
index 0cd56333f504..d5534c3257a4 100644
--- a/testing/web-platform/tests/element-timing/background-image-stretched.html
+++ b/testing/web-platform/tests/element-timing/background-image-stretched.html
@@ -18,9 +18,7 @@ body {
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/buffer-before-onload.html b/testing/web-platform/tests/element-timing/buffer-before-onload.html
index d675c75ba1a2..79dd64e29779 100644
--- a/testing/web-platform/tests/element-timing/buffer-before-onload.html
+++ b/testing/web-platform/tests/element-timing/buffer-before-onload.html
@@ -13,9 +13,7 @@
   is available from the observer with the buffered flag set to true.
   */
   async_test(function(t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     beforeRender = performance.now();
     const img = document.createElement('img');
     img.src = 'resources/square20.jpg';
diff --git a/testing/web-platform/tests/element-timing/buffered-flag.html b/testing/web-platform/tests/element-timing/buffered-flag.html
index 19c387d26b9c..1fca11787923 100644
--- a/testing/web-platform/tests/element-timing/buffered-flag.html
+++ b/testing/web-platform/tests/element-timing/buffered-flag.html
@@ -12,11 +12,9 @@ body {
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test(t => {
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const beforeRender = performance.now();
     const img = document.createElement('img');
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
     // Initial observer used to know when entry has been dispatched
     new PerformanceObserver(() => {
       // Second observer should require buffered flag to receive the already-dispatched entry.
diff --git a/testing/web-platform/tests/element-timing/cross-origin-element.sub.html b/testing/web-platform/tests/element-timing/cross-origin-element.sub.html
index eef69a1d423a..b5b06f30469b 100644
--- a/testing/web-platform/tests/element-timing/cross-origin-element.sub.html
+++ b/testing/web-platform/tests/element-timing/cross-origin-element.sub.html
@@ -12,9 +12,7 @@ body {
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     let img;
     const pathname = 'http://{{domains[www]}}:{{ports[http][1]}}'
           + '/element-timing/resources/square100.png';
diff --git a/testing/web-platform/tests/element-timing/cross-origin-iframe-element.sub.html b/testing/web-platform/tests/element-timing/cross-origin-iframe-element.sub.html
index 7296cfccfda6..b183fe289aa9 100644
--- a/testing/web-platform/tests/element-timing/cross-origin-iframe-element.sub.html
+++ b/testing/web-platform/tests/element-timing/cross-origin-iframe-element.sub.html
@@ -7,9 +7,7 @@
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done((entryList) => {
         assert_unreached("We should not observe a cross origin element.");
diff --git a/testing/web-platform/tests/element-timing/css-generated-text.html b/testing/web-platform/tests/element-timing/css-generated-text.html
index 1e3a812d1bc2..4b7dea73ca8d 100644
--- a/testing/web-platform/tests/element-timing/css-generated-text.html
+++ b/testing/web-platform/tests/element-timing/css-generated-text.html
@@ -17,9 +17,7 @@ body {
 <script>
   async_test(function (t) {
     const beforeRender = performance.now();
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/disconnect-image.html b/testing/web-platform/tests/element-timing/disconnect-image.html
index fa42397557b9..9c2be0e45ac5 100644
--- a/testing/web-platform/tests/element-timing/disconnect-image.html
+++ b/testing/web-platform/tests/element-timing/disconnect-image.html
@@ -9,9 +9,7 @@
   let beforeRender;
   let img;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/element-only-when-fully-active.html b/testing/web-platform/tests/element-timing/element-only-when-fully-active.html
index 5608685a3421..001430516dc8 100644
--- a/testing/web-platform/tests/element-timing/element-only-when-fully-active.html
+++ b/testing/web-platform/tests/element-timing/element-only-when-fully-active.html
@@ -7,6 +7,9 @@
 <iframe src="resources/iframe-stores-entry.html" id="ifr"></iframe>
 <script>
   let t = async_test('Only expose element attribute for fully active documents');
+  t.step(() => {
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
+  });
   window.triggerTest = t.step_func_done(elementEntry => {
     assert_not_equals(elementEntry.element, null);
     const iframe = document.getElementById('ifr');
diff --git a/testing/web-platform/tests/element-timing/first-letter-background.html b/testing/web-platform/tests/element-timing/first-letter-background.html
index 51e82d473e16..911f0d0f3a15 100644
--- a/testing/web-platform/tests/element-timing/first-letter-background.html
+++ b/testing/web-platform/tests/element-timing/first-letter-background.html
@@ -13,9 +13,7 @@
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const div = document.getElementById('target');
     let textObserved = false;
     let imageObserved = false;
diff --git a/testing/web-platform/tests/element-timing/fixed-id-identifier.html b/testing/web-platform/tests/element-timing/fixed-id-identifier.html
index 00d6d4dd94c4..ae8303f021d7 100644
--- a/testing/web-platform/tests/element-timing/fixed-id-identifier.html
+++ b/testing/web-platform/tests/element-timing/fixed-id-identifier.html
@@ -8,9 +8,7 @@
 <p elementtiming='my_identifier' id='my_id'>Text</p>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/image-TAO.sub.html b/testing/web-platform/tests/element-timing/image-TAO.sub.html
index 0906b361394a..ee2b06179009 100644
--- a/testing/web-platform/tests/element-timing/image-TAO.sub.html
+++ b/testing/web-platform/tests/element-timing/image-TAO.sub.html
@@ -7,9 +7,7 @@
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test(t => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const beforeRender = performance.now();
     const remote_img = 'http://{{domains[www]}}:{{ports[http][1]}}/element-timing/resources/TAOImage.py?'
         + 'origin=' + window.location.origin +'&tao=';
diff --git a/testing/web-platform/tests/element-timing/image-carousel.html b/testing/web-platform/tests/element-timing/image-carousel.html
index dc5d8e8dde89..ce6ac951e249 100644
--- a/testing/web-platform/tests/element-timing/image-carousel.html
+++ b/testing/web-platform/tests/element-timing/image-carousel.html
@@ -26,9 +26,7 @@ body {
 
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const beforeRenderTimes = [];
     let entry_count = 0;
     const entry_count_per_element = [0, 0];
diff --git a/testing/web-platform/tests/element-timing/image-clipped-svg.html b/testing/web-platform/tests/element-timing/image-clipped-svg.html
index 15c78a4cec5e..c8e4a67cea68 100644
--- a/testing/web-platform/tests/element-timing/image-clipped-svg.html
+++ b/testing/web-platform/tests/element-timing/image-clipped-svg.html
@@ -7,9 +7,7 @@
 <script>
 let beforeRender;
 async_test(function (t) {
-  if (!window.PerformanceElementTiming) {
-    assert_unreached("PerformanceElementTiming is not implemented");
-  }
+  assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
   const observer = new PerformanceObserver(
     t.step_func_done(function(entryList) {
       assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/image-data-uri.html b/testing/web-platform/tests/element-timing/image-data-uri.html
index e698bcf1a5d7..afe203ae1bf9 100644
--- a/testing/web-platform/tests/element-timing/image-data-uri.html
+++ b/testing/web-platform/tests/element-timing/image-data-uri.html
@@ -16,9 +16,7 @@ body {
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/image-not-added.html b/testing/web-platform/tests/element-timing/image-not-added.html
index e65d1814b0e7..83a6cc608443 100644
--- a/testing/web-platform/tests/element-timing/image-not-added.html
+++ b/testing/web-platform/tests/element-timing/image-not-added.html
@@ -5,9 +5,7 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(() => {
         // The image should not have caused an entry, so fail test.
diff --git a/testing/web-platform/tests/element-timing/image-not-fully-visible.html b/testing/web-platform/tests/element-timing/image-not-fully-visible.html
index ece7770467d1..c51c24a965a6 100644
--- a/testing/web-platform/tests/element-timing/image-not-fully-visible.html
+++ b/testing/web-platform/tests/element-timing/image-not-fully-visible.html
@@ -14,9 +14,7 @@ body {
   let beforeRender;
   let img;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/image-rect-iframe.html b/testing/web-platform/tests/element-timing/image-rect-iframe.html
index 7441405d7475..a97ed5a85078 100644
--- a/testing/web-platform/tests/element-timing/image-rect-iframe.html
+++ b/testing/web-platform/tests/element-timing/image-rect-iframe.html
@@ -11,9 +11,7 @@ body {
 <script src="/resources/testharnessreport.js"></script>
 <script>
   async_test((t) => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     on_event(window, 'message', e => {
       assert_equals(e.data.length, 1);
       assert_equals(e.data.entryType, 'element');
diff --git a/testing/web-platform/tests/element-timing/image-src-change.html b/testing/web-platform/tests/element-timing/image-src-change.html
index 89b8e1d3f747..e9e13742a650 100644
--- a/testing/web-platform/tests/element-timing/image-src-change.html
+++ b/testing/web-platform/tests/element-timing/image-src-change.html
@@ -13,9 +13,7 @@ body {
 <img src='resources/square100.png' elementtiming='my_image' id='my_id'/>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     let beforeRender = performance.now();
     const img = document.getElementById('my_id');
     let firstCallback = true;
diff --git a/testing/web-platform/tests/element-timing/image-with-css-scale.html b/testing/web-platform/tests/element-timing/image-with-css-scale.html
index 2dbbc0672485..9bd71086a75e 100644
--- a/testing/web-platform/tests/element-timing/image-with-css-scale.html
+++ b/testing/web-platform/tests/element-timing/image-with-css-scale.html
@@ -21,9 +21,7 @@ body {
 <script>
   const beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/image-with-rotation.html b/testing/web-platform/tests/element-timing/image-with-rotation.html
index fcffe4acfa58..64ff942f0cda 100644
--- a/testing/web-platform/tests/element-timing/image-with-rotation.html
+++ b/testing/web-platform/tests/element-timing/image-with-rotation.html
@@ -21,9 +21,7 @@ body {
 <script>
   const beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/images-repeated-resource.html b/testing/web-platform/tests/element-timing/images-repeated-resource.html
index e3fe9b90db11..6090e75f26ec 100644
--- a/testing/web-platform/tests/element-timing/images-repeated-resource.html
+++ b/testing/web-platform/tests/element-timing/images-repeated-resource.html
@@ -20,9 +20,7 @@ body {
   let img;
   let img2;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/invisible-images.html b/testing/web-platform/tests/element-timing/invisible-images.html
index 06d9bfd07a0f..8225996e255b 100644
--- a/testing/web-platform/tests/element-timing/invisible-images.html
+++ b/testing/web-platform/tests/element-timing/invisible-images.html
@@ -16,9 +16,7 @@
 </style>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done((entries) => {
         // The image should not have caused an entry, so fail test.
diff --git a/testing/web-platform/tests/element-timing/multiple-background-images.html b/testing/web-platform/tests/element-timing/multiple-background-images.html
index b29e66c04a70..c2a32c3c8e6b 100644
--- a/testing/web-platform/tests/element-timing/multiple-background-images.html
+++ b/testing/web-platform/tests/element-timing/multiple-background-images.html
@@ -18,9 +18,7 @@ body {
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     let numObservedElements = 0;
     let observedCircle = false;
     let observedSquare = false;
diff --git a/testing/web-platform/tests/element-timing/observe-background-image.html b/testing/web-platform/tests/element-timing/observe-background-image.html
index afc6b5b38d74..e02714b70210 100644
--- a/testing/web-platform/tests/element-timing/observe-background-image.html
+++ b/testing/web-platform/tests/element-timing/observe-background-image.html
@@ -18,9 +18,7 @@ body {
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/observe-child-element.html b/testing/web-platform/tests/element-timing/observe-child-element.html
index 33e92a9abddd..4293e814eb91 100644
--- a/testing/web-platform/tests/element-timing/observe-child-element.html
+++ b/testing/web-platform/tests/element-timing/observe-child-element.html
@@ -12,9 +12,7 @@ body {
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done((entryList) => {
         assert_unreached("Should not have received an entry!");
diff --git a/testing/web-platform/tests/element-timing/observe-elementtiming.html b/testing/web-platform/tests/element-timing/observe-elementtiming.html
index 164cc4f580af..ee8960bd7288 100644
--- a/testing/web-platform/tests/element-timing/observe-elementtiming.html
+++ b/testing/web-platform/tests/element-timing/observe-elementtiming.html
@@ -14,9 +14,7 @@ body {
   let beforeRender;
   let img;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/observe-empty-attribute.html b/testing/web-platform/tests/element-timing/observe-empty-attribute.html
index c115a24cf623..25d3492f73be 100644
--- a/testing/web-platform/tests/element-timing/observe-empty-attribute.html
+++ b/testing/web-platform/tests/element-timing/observe-empty-attribute.html
@@ -7,9 +7,7 @@
 <script>
 let beforeRender;
 async_test(function (t) {
-  if (!window.PerformanceElementTiming) {
-    assert_unreached("PerformanceElementTiming is not implemented");
-  }
+  assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
   let observedImage = false;
   let observedText = false;
   const observer = new PerformanceObserver(
diff --git a/testing/web-platform/tests/element-timing/observe-multiple-images.html b/testing/web-platform/tests/element-timing/observe-multiple-images.html
index 6b5c5d9e3cb2..9a0657aa60fe 100644
--- a/testing/web-platform/tests/element-timing/observe-multiple-images.html
+++ b/testing/web-platform/tests/element-timing/observe-multiple-images.html
@@ -22,9 +22,7 @@ body {
 <script>
   let beforeRender, image1Observed=0, image2Observed=0, image3Observed=0;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func(function(entryList) {
         entryList.getEntries().forEach( entry => {
diff --git a/testing/web-platform/tests/element-timing/observe-shadow-image.html b/testing/web-platform/tests/element-timing/observe-shadow-image.html
index 3e1960dde3bf..1c12c5fe0310 100644
--- a/testing/web-platform/tests/element-timing/observe-shadow-image.html
+++ b/testing/web-platform/tests/element-timing/observe-shadow-image.html
@@ -12,9 +12,7 @@ body {
 <div id='target'></div>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_unreached('Should not observe elements in shadow trees!');
diff --git a/testing/web-platform/tests/element-timing/observe-shadow-text.html b/testing/web-platform/tests/element-timing/observe-shadow-text.html
index cc0cf0bd8239..3167a1225c52 100644
--- a/testing/web-platform/tests/element-timing/observe-shadow-text.html
+++ b/testing/web-platform/tests/element-timing/observe-shadow-text.html
@@ -12,9 +12,7 @@ body {
 <div id='target'></div>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_unreached('Should not observe text elements in shadow trees!');
diff --git a/testing/web-platform/tests/element-timing/observe-svg-image.html b/testing/web-platform/tests/element-timing/observe-svg-image.html
index 8a0f61d6699d..83ca4f40aaeb 100644
--- a/testing/web-platform/tests/element-timing/observe-svg-image.html
+++ b/testing/web-platform/tests/element-timing/observe-svg-image.html
@@ -7,9 +7,7 @@
 <script>
 let beforeRender;
 async_test(function (t) {
-  if (!window.PerformanceElementTiming) {
-    assert_unreached("PerformanceElementTiming is not implemented");
-  }
+  assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
   const observer = new PerformanceObserver(
     t.step_func_done(function(entryList) {
       assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/observe-text.html b/testing/web-platform/tests/element-timing/observe-text.html
index 4508db3a5442..a054b2617261 100644
--- a/testing/web-platform/tests/element-timing/observe-text.html
+++ b/testing/web-platform/tests/element-timing/observe-text.html
@@ -15,9 +15,7 @@ p {
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     let paragraph;
     let beforeRender;
     const observer = new PerformanceObserver(
diff --git a/testing/web-platform/tests/element-timing/observe-video-poster.html b/testing/web-platform/tests/element-timing/observe-video-poster.html
index a6348377099f..f64da173c6f2 100644
--- a/testing/web-platform/tests/element-timing/observe-video-poster.html
+++ b/testing/web-platform/tests/element-timing/observe-video-poster.html
@@ -7,9 +7,7 @@
 <script>
 let beforeRender;
 async_test(function (t) {
-  if (!window.PerformanceElementTiming) {
-    assert_unreached("PerformanceElementTiming is not implemented");
-  }
+  assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
   const observer = new PerformanceObserver(
     t.step_func_done(function(entryList) {
       assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/progressively-loaded-image.html b/testing/web-platform/tests/element-timing/progressively-loaded-image.html
index f156e1a32c48..0d59052cf3ac 100644
--- a/testing/web-platform/tests/element-timing/progressively-loaded-image.html
+++ b/testing/web-platform/tests/element-timing/progressively-loaded-image.html
@@ -14,9 +14,7 @@
   let numInitial = 75;
   let sleep = 500;
   async_test(function(t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const img_src = 'resources/progressive-image.py?name=square20.jpg&numInitial='
       + numInitial + '&sleep=' + sleep;
     const observer = new PerformanceObserver(
diff --git a/testing/web-platform/tests/element-timing/rectangular-image.html b/testing/web-platform/tests/element-timing/rectangular-image.html
index 0c09911c5023..a97c549a9aad 100644
--- a/testing/web-platform/tests/element-timing/rectangular-image.html
+++ b/testing/web-platform/tests/element-timing/rectangular-image.html
@@ -14,9 +14,7 @@ body {
   let beforeRender;
   let img;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/element-timing/redirects-tao-star.html b/testing/web-platform/tests/element-timing/redirects-tao-star.html
index a93fcd50ac37..f8e4d19bd07c 100644
--- a/testing/web-platform/tests/element-timing/redirects-tao-star.html
+++ b/testing/web-platform/tests/element-timing/redirects-tao-star.html
@@ -11,9 +11,7 @@
 <body>
 <script>
 async_test(t => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     let destUrl = get_host_info().HTTP_REMOTE_ORIGIN
             + '/resource-timing/resources/multi_redirect.py?';
     destUrl += 'page_origin=' +  get_host_info().HTTP_ORIGIN;
diff --git a/testing/web-platform/tests/element-timing/retrievability.html b/testing/web-platform/tests/element-timing/retrievability.html
index 3ac04d827851..5c6113bdc933 100644
--- a/testing/web-platform/tests/element-timing/retrievability.html
+++ b/testing/web-platform/tests/element-timing/retrievability.html
@@ -7,9 +7,7 @@
 <script>
   let img;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const beforeRender = performance.now();
     new PerformanceObserver(
       t.step_func_done(function(entryList) {
diff --git a/testing/web-platform/tests/element-timing/scroll-to-text.html b/testing/web-platform/tests/element-timing/scroll-to-text.html
index ed332740323b..ca06e91c530a 100644
--- a/testing/web-platform/tests/element-timing/scroll-to-text.html
+++ b/testing/web-platform/tests/element-timing/scroll-to-text.html
@@ -15,9 +15,7 @@
 <p elementtiming='observeMe'>Test text</p>
 <script>
   async_test((t) => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(t.step_func_done(() => {}));
     observer.observe({type: 'element', buffered: true});
     window.onload = () => {
diff --git a/testing/web-platform/tests/element-timing/text-with-display-style.html b/testing/web-platform/tests/element-timing/text-with-display-style.html
index 03939473be33..faf644fd8d24 100644
--- a/testing/web-platform/tests/element-timing/text-with-display-style.html
+++ b/testing/web-platform/tests/element-timing/text-with-display-style.html
@@ -21,9 +21,7 @@ h3 {
 <h3 id='title3' elementtiming='h3'>I am h3</h3>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const beforeRender = performance.now();
     let observedFlex = false;
     let observedGrid = false;
diff --git a/testing/web-platform/tests/element-timing/toJSON.html b/testing/web-platform/tests/element-timing/toJSON.html
index d98893470811..ba13a0fa9079 100644
--- a/testing/web-platform/tests/element-timing/toJSON.html
+++ b/testing/web-platform/tests/element-timing/toJSON.html
@@ -8,9 +8,7 @@
 <img elementtiming='img' src="resources/square100.png"/>
 <script>
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_precondition(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/testing/web-platform/tests/largest-contentful-paint/contracted-image.html b/testing/web-platform/tests/largest-contentful-paint/contracted-image.html
index 2d4a84bf35cf..ed6adfb2c7c6 100644
--- a/testing/web-platform/tests/largest-contentful-paint/contracted-image.html
+++ b/testing/web-platform/tests/largest-contentful-paint/contracted-image.html
@@ -13,9 +13,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
diff --git a/testing/web-platform/tests/largest-contentful-paint/cross-origin-image.sub.html b/testing/web-platform/tests/largest-contentful-paint/cross-origin-image.sub.html
index 58e636e51b9f..be0c8a1e11e3 100644
--- a/testing/web-platform/tests/largest-contentful-paint/cross-origin-image.sub.html
+++ b/testing/web-platform/tests/largest-contentful-paint/cross-origin-image.sub.html
@@ -7,9 +7,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
diff --git a/testing/web-platform/tests/largest-contentful-paint/expanded-image.html b/testing/web-platform/tests/largest-contentful-paint/expanded-image.html
index 6f7043dd8e42..e0b3545c21c2 100644
--- a/testing/web-platform/tests/largest-contentful-paint/expanded-image.html
+++ b/testing/web-platform/tests/largest-contentful-paint/expanded-image.html
@@ -13,9 +13,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
diff --git a/testing/web-platform/tests/largest-contentful-paint/first-letter-background.html b/testing/web-platform/tests/largest-contentful-paint/first-letter-background.html
index 44d2a1a96808..5269e468558b 100644
--- a/testing/web-platform/tests/largest-contentful-paint/first-letter-background.html
+++ b/testing/web-platform/tests/largest-contentful-paint/first-letter-background.html
@@ -12,9 +12,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     const observer = new PerformanceObserver(
       t.step_func(function(entryList) {
diff --git a/testing/web-platform/tests/largest-contentful-paint/first-paint-equals-lcp-text.html b/testing/web-platform/tests/largest-contentful-paint/first-paint-equals-lcp-text.html
index a49a83f346d5..7a01cb15943a 100644
--- a/testing/web-platform/tests/largest-contentful-paint/first-paint-equals-lcp-text.html
+++ b/testing/web-platform/tests/largest-contentful-paint/first-paint-equals-lcp-text.html
@@ -6,12 +6,8 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.PerformancePaintTiming) {
-      assert_unreached("PerformancePaintTiming is not implemented");
-    }
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.PerformancePaintTiming, "PerformancePaintTiming is not implemented");
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     let firstPaintTime = 0;
     let firstContentfulPaintTime = 0;
     let largestContentfulPaintTime = 0;
diff --git a/testing/web-platform/tests/largest-contentful-paint/iframe-content-not-observed.html b/testing/web-platform/tests/largest-contentful-paint/iframe-content-not-observed.html
index 7cb23ddbd205..ea8e0d79f380 100644
--- a/testing/web-platform/tests/largest-contentful-paint/iframe-content-not-observed.html
+++ b/testing/web-platform/tests/largest-contentful-paint/iframe-content-not-observed.html
@@ -8,9 +8,7 @@
 <body>
 <script>
   async_test((t) => {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(entryList => {
         assert_unreached("Should not have received an entry!");
diff --git a/testing/web-platform/tests/largest-contentful-paint/image-src-change.html b/testing/web-platform/tests/largest-contentful-paint/image-src-change.html
index 5ec860fa06f3..cbe46f402b4e 100644
--- a/testing/web-platform/tests/largest-contentful-paint/image-src-change.html
+++ b/testing/web-platform/tests/largest-contentful-paint/image-src-change.html
@@ -8,9 +8,7 @@
 <img src='/images/blue.png' id='image_id'/>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     let beforeLoad = performance.now();
     let firstCallback = true;
     const observer = new PerformanceObserver(
diff --git a/testing/web-platform/tests/largest-contentful-paint/invisible-images.html b/testing/web-platform/tests/largest-contentful-paint/invisible-images.html
index d536f86dcf69..49324663f226 100644
--- a/testing/web-platform/tests/largest-contentful-paint/invisible-images.html
+++ b/testing/web-platform/tests/largest-contentful-paint/invisible-images.html
@@ -19,9 +19,7 @@
 <body>
 <script>
   async_test(t => {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const observer = new PerformanceObserver(
       t.step_func(entryList => {
         entryList.getEntries().forEach(entry => {
diff --git a/testing/web-platform/tests/largest-contentful-paint/larger-image.html b/testing/web-platform/tests/largest-contentful-paint/larger-image.html
index 094c2096752f..a571b8afe791 100644
--- a/testing/web-platform/tests/largest-contentful-paint/larger-image.html
+++ b/testing/web-platform/tests/largest-contentful-paint/larger-image.html
@@ -13,9 +13,7 @@
 <p>More text!</p>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     const observer = new PerformanceObserver(
       t.step_func(entryList => {
diff --git a/testing/web-platform/tests/largest-contentful-paint/larger-text.html b/testing/web-platform/tests/largest-contentful-paint/larger-text.html
index 973832ca6c86..af8bbc06b32c 100644
--- a/testing/web-platform/tests/largest-contentful-paint/larger-text.html
+++ b/testing/web-platform/tests/largest-contentful-paint/larger-text.html
@@ -18,9 +18,7 @@
 <img src='/images/green-2x2.png'/>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     let beforeRender;
     const observer = new PerformanceObserver(
       t.step_func(entryList => {
diff --git a/testing/web-platform/tests/largest-contentful-paint/loadTime-after-appendChild.html b/testing/web-platform/tests/largest-contentful-paint/loadTime-after-appendChild.html
index 0e40127b5768..f320b03df4da 100644
--- a/testing/web-platform/tests/largest-contentful-paint/loadTime-after-appendChild.html
+++ b/testing/web-platform/tests/largest-contentful-paint/loadTime-after-appendChild.html
@@ -7,9 +7,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     let beforeLoad;
     const observer = new PerformanceObserver(
       t.step_func_done(entryList => {
diff --git a/testing/web-platform/tests/largest-contentful-paint/observe-after-untrusted-scroll.html b/testing/web-platform/tests/largest-contentful-paint/observe-after-untrusted-scroll.html
index 1b2cd1d25b5b..4a1a214c8330 100644
--- a/testing/web-platform/tests/largest-contentful-paint/observe-after-untrusted-scroll.html
+++ b/testing/web-platform/tests/largest-contentful-paint/observe-after-untrusted-scroll.html
@@ -7,9 +7,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
diff --git a/testing/web-platform/tests/largest-contentful-paint/observe-image.html b/testing/web-platform/tests/largest-contentful-paint/observe-image.html
index 5856795cac49..58eb5364a925 100644
--- a/testing/web-platform/tests/largest-contentful-paint/observe-image.html
+++ b/testing/web-platform/tests/largest-contentful-paint/observe-image.html
@@ -7,9 +7,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
diff --git a/testing/web-platform/tests/largest-contentful-paint/observe-text.html b/testing/web-platform/tests/largest-contentful-paint/observe-text.html
index a2a376fde335..402fcd801958 100644
--- a/testing/web-platform/tests/largest-contentful-paint/observe-text.html
+++ b/testing/web-platform/tests/largest-contentful-paint/observe-text.html
@@ -11,9 +11,7 @@ p {
 </style>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     let beforeRender;
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
diff --git a/testing/web-platform/tests/largest-contentful-paint/repeated-image.html b/testing/web-platform/tests/largest-contentful-paint/repeated-image.html
index 82d662d330ab..8c3c89090992 100644
--- a/testing/web-platform/tests/largest-contentful-paint/repeated-image.html
+++ b/testing/web-platform/tests/largest-contentful-paint/repeated-image.html
@@ -13,9 +13,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     let beforeLoad = performance.now();
     let firstCallback = true;
     const url = window.location.origin + '/images/black-rectangle.png';
diff --git a/testing/web-platform/tests/largest-contentful-paint/text-with-display-style.html b/testing/web-platform/tests/largest-contentful-paint/text-with-display-style.html
index 2f1f254d7775..24541541a8be 100644
--- a/testing/web-platform/tests/largest-contentful-paint/text-with-display-style.html
+++ b/testing/web-platform/tests/largest-contentful-paint/text-with-display-style.html
@@ -12,9 +12,7 @@
 <h1 id='title'>I am a title!</h1>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     let beforeRender;
     /* In this test, we first observe a header with style 'display: flex'.
      * Once observed, we remove it and add a header with style 'display: grid'.
diff --git a/testing/web-platform/tests/largest-contentful-paint/toJSON.html b/testing/web-platform/tests/largest-contentful-paint/toJSON.html
index 7defcce1b6f9..25be5eb2dc90 100644
--- a/testing/web-platform/tests/largest-contentful-paint/toJSON.html
+++ b/testing/web-platform/tests/largest-contentful-paint/toJSON.html
@@ -7,9 +7,7 @@
 <p>Text!</p>
 <script>
   async_test(function (t) {
-    if (!window.LargestContentfulPaint) {
-      assert_unreached("LargestContentfulPaint is not implemented");
-    }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         const entry = entryList.getEntries()[0];
diff --git a/testing/web-platform/tests/largest-contentful-paint/video-poster.html b/testing/web-platform/tests/largest-contentful-paint/video-poster.html
index 9ad9c4cdfd09..535f30e25657 100644
--- a/testing/web-platform/tests/largest-contentful-paint/video-poster.html
+++ b/testing/web-platform/tests/largest-contentful-paint/video-poster.html
@@ -6,9 +6,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
 async_test(function (t) {
-  if (!window.LargestContentfulPaint) {
-    assert_unreached("LargestContentfulPaint is not implemented");
-  }
+    assert_precondition(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
   const beforeLoad = performance.now();
   const observer = new PerformanceObserver(
     t.step_func_done(function(entryList) {
-- 
2.11.4.GIT