Update overlay scrollbars

Compute solid-color scrollbar properties on all platforms.

It's unnecessary to gate solid-color scrollbar properties on whether
the root container masks to bounds, since the vertical adjust should
resolve to zero in this case anyway.  It's necessary to set VisibleToTotalLengthRatio
for desktop overlay scrollbars to be sized correctly.

BUG=331605
TEST=None
R=aelias

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=243721

[aelias_OOO_until_Jul13, 2014-01-06 23:58:57]

lgtm.  I went ahead and updated your patch description to explain what this is
doing.

[commit-bot: I haz the power, 2014-01-07 00:03:00]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/davemoore@chromium.org/106733005/1

[commit-bot: I haz the power, 2014-01-07 10:08:00]

Retried try job too often on linux_rel for step(s) cc_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2014-01-07 15:07:31]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/davemoore@chromium.org/106733005/1

[commit-bot: I haz the power, 2014-01-07 15:29:22]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/davemoore@chromium.org/106733005/1

[commit-bot: I haz the power, 2014-01-07 16:37:47]

Retried try job too often on linux_rel for step(s) cc_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[aelias_OOO_until_Jul13, 2014-01-07 19:45:40]

Looks like the extra NoteLayerPropertyChanged is causing extra damage that makes
the unit tests fail.  I'd suggest making SetVisibleToTotalLengthRatio virtual
and moving the implementation to SolidColorScrollbarLayerImpl, I expect that
would fix it.

[DaveMoore, 2014-01-08 21:16:57]

Add IsThumbResizable() method to allow PaintedScrollbarLayerImpl to avoid paint
damage when ratio changed

[DaveMoore, 2014-01-08 21:18:20]

PTAL: added IsThumbResizable() method to allow PaintedScrollbarLayerImpl to
avoid extra paints.

[aelias_OOO_until_Jul13, 2014-01-08 22:30:17]

lgtm

https://codereview.chromium.org/106733005/diff/500001/cc/layers/scrollbar_lay...
File cc/layers/scrollbar_layer_impl_base.h (right):

https://codereview.chromium.org/106733005/diff/500001/cc/layers/scrollbar_lay...
cc/layers/scrollbar_layer_impl_base.h:67: // Indicates whether the thumb
represents the visible to total length ratio.
I'd make this say "whether the thumb length can be changed without going back to
the main thread".

[DaveMoore, 2014-01-08 22:35:14]

Comment change

[commit-bot: I haz the power, 2014-01-08 22:37:27]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/davemoore@chromium.org/106733005/570001

[commit-bot: I haz the power, 2014-01-09 01:11:37]

Change committed as 243721