The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5ed7b147c2631389d601d99c831b56f17e0511be

commit 5ed7b147c2631389d601d99c831b56f17e0511be
Author: Tien-Ren Chen <trchen@chromium.org>
Date: Wed May 09 01:35:25 2018

[BlinkGenPropertyTrees] Add contents layer support

This CL adds code to collect contents layers as foreign layers for
BlinkGenPropertyTrees mode. Most layout tests involving canvas /
composited images / video / plugins should now pass. Composited
scrollbars should also draw, though the thumb position may not be
synchronized.

BUG= 840037 

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I905b4b30136fcbc30133fc50f0133a46d3f922ee
Reviewed-on: https://chromium-review.googlesource.com/1048841
Commit-Queue: Tien-Ren Chen <trchen@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557053}
[modify] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/WebKit/LayoutTests/FlagExpectations/enable-blink-gen-property-trees
[add] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/WebKit/LayoutTests/flag-specific/enable-blink-gen-property-trees/compositing/overflow/scrollbar-layer-placement-expected.txt
[modify] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/blink/renderer/core/frame/local_frame_view.cc
[modify] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/blink/renderer/platform/graphics/compositing/paint_artifact_compositor.cc
[modify] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/blink/renderer/platform/graphics/graphics_layer.h
[modify] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/blink/renderer/platform/graphics/paint/display_item.cc
[modify] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/blink/renderer/platform/graphics/paint/display_item.h
[modify] https://crrev.com/5ed7b147c2631389d601d99c831b56f17e0511be/third_party/blink/renderer/platform/testing/paint_test_configurations.h