Disable WorkerTest::QueuedSharedWorkerShutdown.

Disable test for all platforms since it is already disabled for Windows
and is not acting flaky on Mac.

BUG=212339
TBR=dmichael

Review URL: https://codereview.chromium.org/33653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229906 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229906