r=aaronl, sr=peterv fix the wrong type cast in nsRootAccessible::AddAccessibleEventListener and get rid of the strong pointer to nsHTMLIFrameAccessible in nsHTMLIFrameRootAccessible git-svn-id: svn://10.0.0.236/trunk@135495 18797224-902f-48f8-a5cc-f745e15eee43