Fixing frame_rate test so that it will not fail the perf and GPU waterfalls.
Fixing frame_rate test so that it will not fail the perf and GPU waterfalls.

1. Reorganizing the frame_rate test to limit the tests that get performed on the Perf waterfall
2. Adding the --enable-gpu flag to be used by the GPU waterfall for executing GPU-specific tests
3. Reaquiring the active tab after initial page load since it may have been invalidated by a page re-direct.

BUG=102428
TEST=frame_rate test on perf and gpu waterfalls.
REVIEW=http://codereview.chromium.org/8386014/
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=108528
Review URL: http://codereview.chromium.org/8386014

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@108556 0039d316-1c4b-4281-b951-d872f2087c98

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