Add a TODO to WebViewTest.Dialog_TestConfirmDialogDefaultGCCancel regarding its time out behaviour.

TBR=fsamuel
BUG=314809

Review URL: https://codereview.chromium.org/56023010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232793 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232793