Bug 1528828 [wpt PR 15449] - [css-tables] Add some subpixel collapsed border tests...

Bug 1528828 [wpt PR 15449] - [css-tables] Add some subpixel collapsed border tests, a=testonly

Automatic update from web-platform-tests
[css-tables] Add some subpixel collapsed border tests

This CL contains tests only, no behavior change.

Chrome passes only 001, no matter the device pixels.
Safari-lodpi and Firefox-lodpi pass only 001 and 002.
EdgeHTML 18.17763-lodpi, Firefox-hidpi, and Safari-hidpi pass 001, 002,
and 003.

From a plain reading of the tables spec the 003 test is correct. But
given its rampant failure (only EdgeHTML passes when 1x device pixel per
CSS pixel), it'd be reasonable to codify the current empirical behavior
somewhere, if it's not already in a place that I missed.

Chrome probably passes 001 but fails 002 because of LayoutUnit's 1/64
pixel precision but that's not confirmed.

Note that these tests will become invalid if the proposal in
https://github.com/w3c/csswg-drafts/issues/606 is adopted.

Bug: 377847
Change-Id: Ifc9e8f9f878f7462cb949670350eadb17c7c2940
Reviewed-on: https://chromium-review.googlesource.com/c/1477334
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: David Grogan <dgrogan@chromium.org>
Commit-Queue: David Grogan <dgrogan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633538}

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wpt-commits: 41a8506f54e688d655e662f59584dcbf777990f2
wpt-pr: 15449