Use floor time to limit requestAnimationFrame in compositing mode if there are no swaps pending
Use floor time to limit requestAnimationFrame in compositing mode if there are no swaps pending

BUG=114914
TEST=load a page that triggers the compositor and uses rAF but doesn't
cause damage. the callback rate should still be ~60fps


Review URL: http://codereview.chromium.org/9567038

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@124731 0039d316-1c4b-4281-b951-d872f2087c98

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