The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f556cef44f474c02e486e7c3e4eec685dc50794c

commit f556cef44f474c02e486e7c3e4eec685dc50794c
Author: chrishtr <chrishtr@chromium.org>
Date: Sat May 13 05:31:01 2017

Fix cc scrollbar layer issues with initialization, and use element ids throughout.

1. Previously, there was an issue with initialization paths for cc scrollbar
layers, which may be created when property trees are in an inconsistent state.
Now we never try to update property tree opacity during construction, and
also pass correct initial opacities from the pending tree rather than assuming
0.0f.

2. Deleted workaround code to bail out during the condition #1 described above.

3. Removed always_use_active_tree_opacity_effect_ids and corresponding methods
on layers, in favor of re-using the existing list of scrollbar animation
controllers on LayerTreeHostImpl. It turned out that there was an exact match
between the layers put in always_use_active_tree_opacity_effect_ids and scrollbars.
This also removes another instance of looking up effect id by node.

4. Start always setting ElementId on scrollbar layers, to support #3 above.
To do this, added a new namespace for CompsitorElementId, and also performed
some related cleanup along the way.

BUG= 718564 , 702832 
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2877033002
Cr-Commit-Position: refs/heads/master@{#471564}

[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/blink/web_scrollbar_layer_impl.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/blink/web_scrollbar_layer_impl.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/input/scrollbar_animation_controller.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/input/scrollbar_animation_controller.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/input/scrollbar_animation_controller_unittest.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/layer.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/layer.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/painted_overlay_scrollbar_layer.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/painted_overlay_scrollbar_layer.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/painted_scrollbar_layer.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/painted_scrollbar_layer.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/scrollbar_layer_impl_base.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/scrollbar_layer_unittest.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/solid_color_scrollbar_layer.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/layers/solid_color_scrollbar_layer.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/layer_tree_host_impl.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/layer_tree_host_impl.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/layer_tree_host_impl_unittest.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/layer_tree_impl.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/layer_tree_impl.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/property_tree.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/property_tree.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/cc/trees/property_tree_builder.cc
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/animation/Animation.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/animation/AnimationTest.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/animation/CompositorAnimations.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/frame/VisualViewport.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/page/scrolling/ScrollState.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/platform/graphics/CompositorElementId.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/platform/graphics/CompositorElementId.h
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/platform/graphics/CompositorElementIdTest.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/platform/graphics/CompositorMutableStateProvider.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/platform/graphics/CompositorMutableStateTest.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/web/LinkHighlightImpl.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/Source/web/tests/VisualViewportTest.cpp
[modify] https://crrev.com/f556cef44f474c02e486e7c3e4eec685dc50794c/third_party/WebKit/public/platform/WebScrollbarLayer.h

Chris, are you still working on this or should someone pick it up?

It should be done, but the comment on lines 63-64 of scrollbar_layer_impl_base.h
needs to be updated. Go ahead and take it if you want to land that patch.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0a5466013c7af978cf4c8271d1cf307241d93dc8

commit 0a5466013c7af978cf4c8271d1cf307241d93dc8
Author: Chris Harrelson <chrishtr@chromium.org>
Date: Wed Aug 23 23:40:30 2017

Remove obsolete comment.

Bug:  702832 
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Id2460718f226b85ba7068b6ad9a635394a4c49b6
Reviewed-on: https://chromium-review.googlesource.com/629967
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Walter Korman <wkorman@chromium.org>
Reviewed-by: Walter Korman <wkorman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496869}
[modify] https://crrev.com/0a5466013c7af978cf4c8271d1cf307241d93dc8/cc/layers/scrollbar_layer_impl_base.h