I rebasedlined that test recently for small pixel differences. I'm sure it's that, and nothing really to fix here.

Actually no. This one does absolute pixel comparisons and doesn't have a reference image. The left square is supposed to render dark brown if the premultipliedAlpha flag is being honored correctly on the canvas's layer, but in this mode – which is admittedly not the default – it renders as dark green. I need to dig in and make sure that the GLRenderer is doing the right thing in its shaders.

Ohh okay! Thanks

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b3a47fa27afa8ddac63c2ee289e6d9ca38eda8ae

commit b3a47fa27afa8ddac63c2ee289e6d9ca38eda8ae
Author: Kenneth Russell <kbr@chromium.org>
Date: Tue Jan 30 21:44:50 2018

Fix premultipliedAlpha:false with OpenGL renderer.

The setting of the CC layer's PremultipliedAlpha flag was (still!)
wrong in the case where the workaround was taking effect.

Added a new test to catch this. Currently Mac-specific; ChromeOS is
the only other platform that could catch it and there aren't any such
machines on the GPU waterfalls.

Bug:  804061 
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Ib71832e48d4880defba01f675806294066eb2e4f
Reviewed-on: https://chromium-review.googlesource.com/887967
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533030}
[modify] https://crrev.com/b3a47fa27afa8ddac63c2ee289e6d9ca38eda8ae/content/test/gpu/gpu_tests/pixel_test_pages.py
[modify] https://crrev.com/b3a47fa27afa8ddac63c2ee289e6d9ca38eda8ae/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp