Re-enable tab switching test.
Re-enable tab switching test.

After some debugging on the interactive perf system, it
appears the screen was locked (or at least locked up).
Current theory is this is why OnPaint wasn't being
called and the histogram wasn't being populated.

BUG=28968
TEST=tab switching test runs on slaves

Review URL: http://codereview.chromium.org/463053

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@34093 0039d316-1c4b-4281-b951-d872f2087c98

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