Fixes up the race condition that exists with deleting a file vs watching it.

      The tests created a file and attempted to hook a watcher on it on a separate thread
but it was deleting it before the thread had a chance to watch it.

BUG=77217, 77064, 69641, 76987
TEST=BUILD

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=79307

Review URL: http://codereview.chromium.org/6676118

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@80205 0039d316-1c4b-4281-b951-d872f2087c98