Enable WorkerTest.WorkerClose.

      It was disabled before due to worker termination issues (http://crbug.com/36630) but those were fixed upstream.
BUG=36630
TEST=none

Review URL: http://codereview.chromium.org/1763007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@45382 0039d316-1c4b-4281-b951-d872f2087c98