Stop trusting the sign-in process if it manages to navigate to another URL.

      BUG=252062
TEST=See bug
R=tim@chromium.org

Review URL: https://codereview.chromium.org/17727002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@208589 0039d316-1c4b-4281-b951-d872f2087c98