GitLab

If the test exits before the navigation completes, the alert may cause
difficulties. Use PUTs instead for an abort which does not trigger UI or
anything.  Re-enable the tests on OS X as that was probably the cause for the
flake.

BUG=142535,142912
TEST=PrerenderBrowserTest.ControlGroup,
     PrerenderBrowserTest.MatchCompleteDummy

Review URL: https://codereview.chromium.org/132643002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244095 0039d316-1c4b-4281-b951-d872f2087c98