Ensure PaintArtifactCompositor assigns a scroll tree index to all cc layers

Ensure PaintArtifactCompositor assigns a scroll tree index to all cc layers

[1] introduced a bug where the scroll tree index of a cc layer would
only be set for scrolling layers, and left as -1 otherwise. This
introduced a crash when doing impl-side hit testing for scroll events.

This patch extracts the nearestScrollNode logic from PaintLayer.cpp
and uses it for both PaintLayer and PaintArtifactCompositor. A
comment has been added warning of the performance implications.

[1] https://chromium.googlesource.com/chromium/src/+/3eee970eb6757c6ea3997e0722d7bab727b9c11c

BUG=687019
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2667373002
Cr-Commit-Position: refs/heads/master@{#447854}
Committed: https://chromium.googlesource.com/chromium/src/+/06f6cd0653d33dc0e087cf3aede5df399ffc9db0

[pdr., 2017-02-02 04:20:09]

The CQ bit was checked by pdr@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-02-02 04:20:29]

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

[pdr., 2017-02-02 04:20:30]

pdr@chromium.org changed reviewers:
+ wkorman@chromium.org

[pdr., 2017-02-02 04:22:32]

https://codereview.chromium.org/2667373002/diff/1/third_party/WebKit/Source/p...
File
third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp
(right):

https://codereview.chromium.org/2667373002/diff/1/third_party/WebKit/Source/p...
third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp:745:
EXPECT_EQ(scrollTransformNode.id, contentLayerAt(0)->transform_tree_index());
There is not yet any end-to-end infrastructure for impl-side hit testing so a
simple unit test has been added instead. I'm not a huge fan of this but
discussed it with Ajuma and we think it's a reasonable approach for now. For
ease of sleeping I am telling myself the test does add some coverage of
PaintArtifactCompositor setting scroll and transform values on cc:layer that
wasn't present before.

[commit-bot: I haz the power, 2017-02-02 06:29:27]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-02-02 06:29:27]

Dry run: This issue passed the CQ dry run.

[wkorman, 2017-02-02 21:37:29]

lgtm

[pdr., 2017-02-02 21:56:36]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2017-02-02 21:57:17]

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, 2017-02-02 22:03:53]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1486072596857820, "parent_rev":
"f2095b9da969dd7decf3224fc96ffe8ef5f5455b", "commit_rev":
"06f6cd0653d33dc0e087cf3aede5df399ffc9db0"}

[commit-bot: I haz the power, 2017-02-02 22:05:31]

Description was changed from

==========
Ensure PaintArtifactCompositor assigns a scroll tree index to all cc layers

[1] introduced a bug where the scroll tree index of a cc layer would
only be set for scrolling layers, and left as -1 otherwise. This
introduced a crash when doing impl-side hit testing for scroll events.

This patch extracts the nearestScrollNode logic from PaintLayer.cpp
and uses it for both PaintLayer and PaintArtifactCompositor. A
comment has been added warning of the performance implications.

[1]
https://chromium.googlesource.com/chromium/src/+/3eee970eb6757c6ea3997e0722d7...

BUG=687019
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Ensure PaintArtifactCompositor assigns a scroll tree index to all cc layers

[1] introduced a bug where the scroll tree index of a cc layer would
only be set for scrolling layers, and left as -1 otherwise. This
introduced a crash when doing impl-side hit testing for scroll events.

This patch extracts the nearestScrollNode logic from PaintLayer.cpp
and uses it for both PaintLayer and PaintArtifactCompositor. A
comment has been added warning of the performance implications.

[1]
https://chromium.googlesource.com/chromium/src/+/3eee970eb6757c6ea3997e0722d7...

BUG=687019
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2667373002
Cr-Commit-Position: refs/heads/master@{#447854}
Committed:
https://chromium.googlesource.com/chromium/src/+/06f6cd0653d33dc0e087cf3aede5...
==========

[commit-bot: I haz the power, 2017-02-02 22:05:32]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/06f6cd0653d33dc0e087cf3aede5...