Bug 750820 - make oldFocusedContent an nsCOMPtr in nsGlobalWindow::PageHidden. r=bz

dom/base/nsFocusManager.cpp

@@ -927,8 +927,7 @@ nsFocusManager::WindowHidden(nsIDOMWindow* aWindow)
   // window, or an ancestor of the focused window. Either way, the focus is no
   // longer valid, so it needs to be updated.
 
-  nsIContent* oldFocusedContent = mFocusedContent;
-  mFocusedContent = nsnull;
+  nsCOMPtr<nsIContent> oldFocusedContent = mFocusedContent.forget();
 
   if (oldFocusedContent && oldFocusedContent->IsInDoc()) {
     NotifyFocusStateChange(oldFocusedContent,