Fix the race condition between mac drawRect and toggling accelerated compositing

Fix the race condition between mac drawRect and toggling accelerated compositing

TBR=jam
BUG=100862
TEST=open Flicker-test2.html from attachment of http://code.google.com/p/chromium/issues/detail?id=77126, verify that the slider widget does not randomly flicker

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=111185

[jbates, 2011-11-19 01:39:36]

This flicker was introduced by the CL that removed CVDisplayLink. This change
chooses whether to drawRect in accelerated mode based on the last SwapBuffers or
DidUpdateBackingStore instead of is_accelerated_compositing which is too
volatile (set by asynchronous IPC).

[Nico, 2011-11-19 01:43:17]

LGTM

Can you think of a good way to test this? (I can't.)

[jbates, 2011-11-19 02:04:40]

On 2011/11/19 01:43:17, Nico wrote:
> LGTM
> 
> Can you think of a good way to test this? (I can't.)

Not sure about an automated test, but Flicker-test2.html has exposed 4 other
bugs as well! It would be a good manual test for QA to run periodically.

[jam, 2011-11-21 18:18:42]

I'm not familiar with mac code. please send this to an owner who is (i.e. avi)

[Nico, 2011-11-21 18:20:25]

On 2011/11/21 18:18:42, John Abd-El-Malek wrote:
> I'm not familiar with mac code. please send this to an owner who is (i.e. avi)

It's been reviewed by someone who is familiar with mac stuff. It only needs a
content review (no bad dependencies etc).

[Nico, 2011-11-22 05:43:33]

jbates: I'd add TBR=jam to the CL description and submit this.