Makes windows repaint scrollbars when position changes

Makes windows repaint scrollbars when position changes

This is needed since arrows draw differently when thumb is at end
points.

BUG=358566
TEST=see bug
R=eseidel@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=171683

[sky, 2014-04-14 22:10:59]

This file doesn't have much history, so I randomly picked you Eric. If you think
there is a better reviewer let me know.

[eseidel, 2014-04-14 22:21:46]

I can't imagine this is the right fix if this just regressed in M35.

Could you provide more explanation as to why this is the right layer to fix this
at?

[eseidel, 2014-04-14 22:23:31]

If we're going to do this, we might as well delete this #define all together, or
change it to be !MAC?

The only code this changes is this:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

I just don't understand why this behavior would need changing for the first time
in M35?

[eseidel, 2014-04-14 22:27:00]

lgtm

Scott tells me that Aura behavior changed in M35.  So yeah, this makes total
sense.

[commit-bot: I haz the power, 2014-04-14 22:27:25]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/237943002/1

[commit-bot: I haz the power, 2014-04-14 22:53:34]

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

[commit-bot: I haz the power, 2014-04-14 22:53:35]

Try jobs failed on following builders:
  tryserver.blink on linux_blink_rel

[sky, 2014-04-15 00:33:03]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-04-15 00:33:21]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/237943002/1

[commit-bot: I haz the power, 2014-04-15 01:02:40]

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

[commit-bot: I haz the power, 2014-04-15 01:02:41]

Try jobs failed on following builders:
  tryserver.blink on win_blink_rel

[sky, 2014-04-15 18:30:21]

Eric, I had to update some layout test expectations. Take another look?

[eseidel, 2014-04-15 18:38:20]

lgtm

Makes sense.  It's sorta silly that blink isn't smart enough to only issue a
full invalidation when you reach an endpoint and always issues a full
invalidation on every thumb move, but whatever.

[commit-bot: I haz the power, 2014-04-15 18:38:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/237943002/20001

[commit-bot: I haz the power, 2014-04-15 19:47:27]

Change committed as 171683