Media Galleries API Picasa: Fix flaky temp dir watch file invalidation test.

BUG=289681
R=vandebo@chromium.org

Review URL: https://codereview.chromium.org/24797002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225819 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225819