cc: Make custom scrollbar scroll on main thread

cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
have a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/599a0d9d885bae01856dc0c716bf851389fe3330
Cr-Commit-Position: refs/heads/master@{#401891}

[sunxd, 2016-06-21 17:57:01]

Description was changed from

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
has a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
==========

to

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
has a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
==========

[sunxd, 2016-06-21 17:58:29]

Description was changed from

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
has a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
==========

to

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
have a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
==========

[sunxd, 2016-06-21 17:58:29]

sunxd@chromium.org changed reviewers:
+ ajuma@chromium.org, bokan@chromium.org, jaydasika@chromium.org,
vollick@chromium.org

[sunxd, 2016-06-21 17:58:38]

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

[commit-bot: I haz the power, 2016-06-21 17:59:08]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2085853003/1

[sunxd, 2016-06-21 17:59:38]

This fixes the bug. But I'm wondering if there can be any test added.

[commit-bot: I haz the power, 2016-06-21 21:03:41]

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

[commit-bot: I haz the power, 2016-06-21 21:03:43]

Dry run: This issue passed the CQ dry run.

[ajuma, 2016-06-22 14:41:41]

Please add a ScrollingCoordinatorTest for this (see the tests in that file that
check for shouldScrollOnMainThread).

https://codereview.chromium.org/2085853003/diff/1/cc/input/main_thread_scroll...
File cc/input/main_thread_scrolling_reason.h (right):

https://codereview.chromium.org/2085853003/diff/1/cc/input/main_thread_scroll...
cc/input/main_thread_scrolling_reason.h:45: kHasStickyPositionObjects |
kCustomScrollbarScrolling;
Would it make sense to just reuse kScrollbarScrolling instead of adding a new
reason?

https://codereview.chromium.org/2085853003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
(right):

https://codereview.chromium.org/2085853003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp:346:
scrollbarGraphicsLayer->platformLayer()->addMainThreadScrollingReasons(MainThreadScrollingReason::kCustomScrollbarScrolling);
I think you also need an 'else' case to remove the main-thread scrolling reason
(to handle the case of a scrollbar that switches from custom to non-custom).

[ajuma, 2016-06-24 13:42:00]

Thanks, lgtm

[bokan, 2016-06-24 14:16:41]

lgtm

[sunxd, 2016-06-24 14:34:30]

The CQ bit was checked by sunxd@chromium.org

[sunxd, 2016-06-24 14:34:33]

The CQ bit was unchecked by sunxd@chromium.org

[sunxd, 2016-06-24 14:34:36]

The CQ bit was unchecked by sunxd@chromium.org

[sunxd, 2016-06-24 14:34:53]

The CQ bit was checked by sunxd@chromium.org

[commit-bot: I haz the power, 2016-06-24 14:35:09]

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, 2016-06-24 17:34:37]

Description was changed from

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
have a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
==========

to

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
have a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
==========

[commit-bot: I haz the power, 2016-06-24 17:34:39]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2016-06-24 17:35:56]

Description was changed from

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
have a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
==========

to

==========
cc: Make custom scrollbar scroll on main thread

The compositor hit testing needs to let the main thread deal with
scrolling on a scrollbar layer. However some webpages on high-DPI screen
have a custom scrollbar. The compositor cannot figure out if a layer is
a custom scrollbar as it is only a GraphicsLayer in blink.

This CL forces custom scrollbars scroll on main thread so that gestures
on scrollbars can be correctly processed.

BUG=618183
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/599a0d9d885bae01856dc0c716bf851389fe3330
Cr-Commit-Position: refs/heads/master@{#401891}
==========

[commit-bot: I haz the power, 2016-06-24 17:35:58]

Patchset 3 (id:??) landed as
https://crrev.com/599a0d9d885bae01856dc0c716bf851389fe3330
Cr-Commit-Position: refs/heads/master@{#401891}