re-enable performance test
The bugs that caused this test to be unstable have now been fixed or worked around.

BUG=279443

Review URL: https://codereview.chromium.org/26990003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228928 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228928