[Root Layer Scrolls] Fix touch event rect clearing.

[Root Layer Scrolls] Fix touch event rect clearing.

When RLS is enabled, the code that clears out obsolete touch event
rects can miss clearing rects on the root layer's main graphics
layer backing if something caused the root layer to overflow.

Here's the scenario:

- Frame does not overflow.
- Touch event handler is registered.
- ScrollingCoordinator annotates touch event rects to the root layer's
  graphicsLayerBacking, which is its main graphics layer backing,
  because it doesn't overflow.
- Something is added to make the frame overflow.
- Touch event rects are removed from the root layer's
  graphicsLayerBacking, which is now the scrolling content layer.
  The main graphics layer backing, which has a touch event rect from
  the previous frame, is not modified, so keeps its old touch event
  rect.

This patch ensures that touch rects are cleared on both the main
graphics layer and the scrolling contents layer.

BUG=490942
R=skobes@chromium.org
TEST=FrameThrottlingTest with RLS enabled

Review-Url: https://codereview.chromium.org/2664083005
Cr-Commit-Position: refs/heads/master@{#448362}
Committed: https://chromium.googlesource.com/chromium/src/+/1af92770ce1315465a635bb797dd501b97d883bc

[skobes, 2017-02-03 04:29:51]

lgtm w/ nit

https://codereview.chromium.org/2664083005/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
(right):

https://codereview.chromium.org/2664083005/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp:749:
GraphicsLayer* ownGraphicsLayer =
I'd call these mainGraphicsLayer and scrollingContentsLayer for clarity (both
are "owned" by the PaintLayer).

[szager1, 2017-02-06 18:27:07]

The CQ bit was checked by szager@chromium.org

[szager1, 2017-02-06 18:27:07]

The patchset sent to the CQ was uploaded after l-g-t-m from skobes@chromium.org
Link to the patchset: https://codereview.chromium.org/2664083005/#ps20001
(title: "variable renames")

[commit-bot: I haz the power, 2017-02-06 18:27:50]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-06 20:04:12]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1486405627301510,
"parent_rev": "db8ea2e90a1b1de4186209e52c7734f226c7ed7e", "commit_rev":
"1af92770ce1315465a635bb797dd501b97d883bc"}

[commit-bot: I haz the power, 2017-02-06 20:04:47]

Description was changed from

==========
[Root Layer Scrolls] Fix touch event rect clearing.

When RLS is enabled, the code that clears out obsolete touch event
rects can miss clearing rects on the root layer's main graphics
layer backing if something caused the root layer to overflow.

Here's the scenario:

- Frame does not overflow.
- Touch event handler is registered.
- ScrollingCoordinator annotates touch event rects to the root layer's
  graphicsLayerBacking, which is its main graphics layer backing,
  because it doesn't overflow.
- Something is added to make the frame overflow.
- Touch event rects are removed from the root layer's
  graphicsLayerBacking, which is now the scrolling content layer.
  The main graphics layer backing, which has a touch event rect from
  the previous frame, is not modified, so keeps its old touch event
  rect.

This patch ensures that touch rects are cleared on both the main
graphics layer and the scrolling contents layer.

BUG=490942
R=skobes@chromium.org
TEST=FrameThrottlingTest with RLS enabled
==========

to

==========
[Root Layer Scrolls] Fix touch event rect clearing.

When RLS is enabled, the code that clears out obsolete touch event
rects can miss clearing rects on the root layer's main graphics
layer backing if something caused the root layer to overflow.

Here's the scenario:

- Frame does not overflow.
- Touch event handler is registered.
- ScrollingCoordinator annotates touch event rects to the root layer's
  graphicsLayerBacking, which is its main graphics layer backing,
  because it doesn't overflow.
- Something is added to make the frame overflow.
- Touch event rects are removed from the root layer's
  graphicsLayerBacking, which is now the scrolling content layer.
  The main graphics layer backing, which has a touch event rect from
  the previous frame, is not modified, so keeps its old touch event
  rect.

This patch ensures that touch rects are cleared on both the main
graphics layer and the scrolling contents layer.

BUG=490942
R=skobes@chromium.org
TEST=FrameThrottlingTest with RLS enabled

Review-Url: https://codereview.chromium.org/2664083005
Cr-Commit-Position: refs/heads/master@{#448362}
Committed:
https://chromium.googlesource.com/chromium/src/+/1af92770ce1315465a635bb797dd...
==========

[commit-bot: I haz the power, 2017-02-06 20:04:48]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/chromium/src/+/1af92770ce1315465a635bb797dd...