First attempt at fixing a crash that occurs when we get into WebFrameLoaderClient::dispatchDidChangeLocationWithinPage()

      with an empty redirect chain.

BUG=22205
TEST=none


Review URL: http://codereview.chromium.org/326015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@30496 0039d316-1c4b-4281-b951-d872f2087c98