Fix performance regression and bug with hide_scrollbars setting.

Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true (e.g. trigger unnecessary
layouts), because they think that scrollbar existence has changed
even if it didn't.

For FrameView, we can avoid this by enforcing hide_scrollbars
in computeScrollbarExistence instead. For PLSA, we check for
hide_scrollbars in updateAfterLayout to determine if the
scrollbar existence will change.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317, 639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Committed: https://crrev.com/d9b6e52af3a84c562f57a751463cf180d5499928
Cr-Commit-Position: refs/heads/master@{#423671}

[Eric Seckler, 2016-10-06 11:57:52]

Description was changed from

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableLayer may perform more work than
necessary if hide_scrollbars is true, because they may think that
scrollbar visibility has changed.

BUG=652317,639806
==========

to

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableLayer may perform more work than
necessary if hide_scrollbars is true, because they may think that
scrollbar visibility has changed.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Eric Seckler, 2016-10-06 11:57:59]

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

[commit-bot: I haz the power, 2016-10-06 11:58:11]

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

[Eric Seckler, 2016-10-06 12:24:06]

Description was changed from

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableLayer may perform more work than
necessary if hide_scrollbars is true, because they may think that
scrollbar visibility has changed.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true, because they think that
scrollbar visibility has changed even if it didn't.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Eric Seckler, 2016-10-06 12:33:50]

Description was changed from

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true, because they think that
scrollbar visibility has changed even if it didn't.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true (e.g. trigger unnecessary
layouts), because they think that scrollbar existence has changed
even if it didn't.

For FrameView, we can avoid this by enforcing hide_scrollbars
in computeScrollbarExistence instead. For PLSA, we check for
hide_scrollbars in updateAfterLayout to determine if the
scrollbar existence will change.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Eric Seckler, 2016-10-06 12:39:29]

eseckler@chromium.org changed reviewers:
+ skobes@chromium.org

[Eric Seckler, 2016-10-06 12:39:29]

Steve, here's yet another change regarding hide_scrollbars. Sorry it's become
such a mess.

I'm considering refactoring PLSA so that there's a common logic that calculates
scrollbar existence for both updateAfterStyleChange and updateAfterLayout,
similar to what computeScrollbarExistence does in FrameView. Do you think that
makes sense as a follow-up?

Thanks!

[commit-bot: I haz the power, 2016-10-06 13:09:39]

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

[commit-bot: I haz the power, 2016-10-06 13:09:39]

Dry run: This issue passed the CQ dry run.

[skobes, 2016-10-06 19:48:09]

lgtm 

Yes it would be great to have a single place for computing PLSA scrollbar
existence.

Are the perf bots running with hide_scrollbars enabled?  That's a little
concerning (what if we had a scrollbars-correlated perf regression?)

[Eric Seckler, 2016-10-06 20:34:22]

On 2016/10/06 19:48:09, skobes wrote:
> lgtm 
> 
> Yes it would be great to have a single place for computing PLSA scrollbar
> existence.
Sounds good, I'll look into it :)

> Are the perf bots running with hide_scrollbars enabled?  That's a little
> concerning (what if we had a scrollbars-correlated perf regression?)
It's only the android-webview bots that now run with hide_scrollbars enabled,
since https://codereview.chromium.org/2380963002. All other bots continue to
have scrollbars :)

[Eric Seckler, 2016-10-06 20:34:34]

The CQ bit was checked by eseckler@chromium.org

[commit-bot: I haz the power, 2016-10-06 20:35:13]

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, 2016-10-06 20:56:00]

Description was changed from

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true (e.g. trigger unnecessary
layouts), because they think that scrollbar existence has changed
even if it didn't.

For FrameView, we can avoid this by enforcing hide_scrollbars
in computeScrollbarExistence instead. For PLSA, we check for
hide_scrollbars in updateAfterLayout to determine if the
scrollbar existence will change.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true (e.g. trigger unnecessary
layouts), because they think that scrollbar existence has changed
even if it didn't.

For FrameView, we can avoid this by enforcing hide_scrollbars
in computeScrollbarExistence instead. For PLSA, we check for
hide_scrollbars in updateAfterLayout to determine if the
scrollbar existence will change.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[commit-bot: I haz the power, 2016-10-06 20:56:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-06 20:59:56]

Description was changed from

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true (e.g. trigger unnecessary
layouts), because they think that scrollbar existence has changed
even if it didn't.

For FrameView, we can avoid this by enforcing hide_scrollbars
in computeScrollbarExistence instead. For PLSA, we check for
hide_scrollbars in updateAfterLayout to determine if the
scrollbar existence will change.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Fix performance regression and bug with hide_scrollbars setting.

FrameView and PaintLayerScrollableArea may perform more work than
necessary if hide_scrollbars is true (e.g. trigger unnecessary
layouts), because they think that scrollbar existence has changed
even if it didn't.

For FrameView, we can avoid this by enforcing hide_scrollbars
in computeScrollbarExistence instead. For PLSA, we check for
hide_scrollbars in updateAfterLayout to determine if the
scrollbar existence will change.

Also fixes another potential bug in PLSA, which may incorrectly
assume existence of scrollbars if hide_scrollbars is true.

BUG=652317,639806
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Committed: https://crrev.com/d9b6e52af3a84c562f57a751463cf180d5499928
Cr-Commit-Position: refs/heads/master@{#423671}
==========

[commit-bot: I haz the power, 2016-10-06 20:59:57]

Patchset 1 (id:??) landed as
https://crrev.com/d9b6e52af3a84c562f57a751463cf180d5499928
Cr-Commit-Position: refs/heads/master@{#423671}