Bug 1485742 [wpt PR 12649] - Add intrinsicsize attribute to HTMLImageElement behind...

Bug 1485742 [wpt PR 12649] - Add intrinsicsize attribute to HTMLImageElement behind a flag, a=testonly

Automatic update from web-platform-testsAdd intrinsicsize attribute to HTMLImageElement behind a flag

Design doc: https://docs.google.com/document/d/1yh_-ayeaFV0EjuR51U641zbrPAB0Baqj6UrC9bT9iqQ/edit#heading=h.y7amr11fn0tb

This CL implements "intrinsicsize" attribute for HTMLImageElement.
The value of "intrinsicsize" overrides the intrinsic size:

1. When no width and (or) height is specified, the value of
"intrinsicsize" will be used to determine the area to layout the image
content.

2. natualWidth and naturalHeight will return the density corrected
value of "intrinsicsize".

See explainer: https://github.com/ojanvafai/intrinsicsize-attribute/blob/master/README.md

BUG: 874629
Cq-Include-Trybots: luci.chromium.try​:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I519f01841ee3e761b22874dbecd74f7e6843e2a9
Reviewed-on: https://chromium-review.googlesource.com/1150725
Commit-Queue: Luna Lu <loonybear@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#587132}

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wpt-commits: b42438a5382241da291b3284527db833e82590d1
wpt-pr: 12649