[Autofill] Fix MessageLoop in test.

The old approach (RunMessageLoop) only works for dialogs that
actually post messages. This seems to be true for Views, but is
not true for the upcoming OSX dialogs.
R=isherman@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/14136005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@195588 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed