Disable NotificationBitmapFetcherBrowserTest.StartTest

TBR=petewil@chromium.org
BUG=314821

Review URL: https://codereview.chromium.org/57853005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232803 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232803