GitLab

1. Move the code that checks whether FCM and/or ThreadedCompositing is enabled to a separate file (compositor_utils) that can be accessed from all the spots that need the info.
2. Cache results results for checks so that we don't have to check them every frame (string compares were actually showing up in profile results)
3. Some cosmetic changes to variable names to keep them consistent.
4. Re-arranged to code that decides what trials run in which channels.

This CL also enables FCM on beta/stable by default but keeps the previous 1/3 experiment running on the other channels.

BUG=


Review URL: https://chromiumcodereview.appspot.com/10824168

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150359 0039d316-1c4b-4281-b951-d872f2087c98