Performance fixes for CoreAnimation.

Performance fixes for CoreAnimation.

Consolidate the calls to [NSScreen screens] because this call can take
several milliseconds, and use an observer to ensure that this call is
only made when the value is changed.

Only use a single OpenGL context because using multiple contexts does
not improve performance and only adds complexity.

BUG=245900
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=247621

[ccameron, 2014-01-28 09:17:16]

This gets CA performance up where non-CA performance is (and in some cases
better).

Also, WRT the multiple observers for the same action -- feel free to say "create
a global observer, you lazy bum", but, if so, let me know if you'd prefer it in
the same file or a separate file.

There is still a synchronization bug that I'll need to take care of (or
sufficiently rationalize ignoring), and a (IIUC Apple) multi-GPU-related
performance bug, which need to be taken care of before I can turn this on.

[Avi (use Gerrit), 2014-01-28 20:12:06]

The screen calls LGTM, the OpenGL call I don't know enough to review.

Yeah, you could do a single global observer, but is that something that you're
worried about having change on you a lot? Keep it simple; what you've got is
fine.

[ccameron, 2014-01-29 01:07:51]

Thanks.

I'll add kbr (at F2F) to TBR the GL line. There's actually a huge change coming
WRT GL contexts (see http://crbug.com/312462) which I'll need to throw at a GL
person.

I avoided the global observer because it would need to be another singleton
class, and would probably need to be in a separate file and need its lifetime
watched carefully, so it was simpler to just hook into the existing system.

[commit-bot: I haz the power, 2014-01-29 01:08:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ccameron@chromium.org/134753008/20001

[commit-bot: I haz the power, 2014-01-29 05:11:56]

Change committed as 247621