Bug 1543315 - part 9: Mark nsIPresShell::FlushPendingNotifications() as MOZ_CAN_RUN_SCRIPT r=smaug

So, this patch makes all caller of it safe including its arguments unless
they come from other methods.

Differential Revision: https://phabricator.services.mozilla.com/D27225

docshell/base/nsDocShell.cpp

@@ -6578,7 +6578,8 @@ nsresult nsDocShell::EndPageLoad(nsIWebProgress* aProgress,
   // will cause any OnLoad(...) and PopState(...) handlers to fire.
   if (!mEODForCurrentDocument && mContentViewer) {
     mIsExecutingOnLoadHandler = true;
-    mContentViewer->LoadComplete(aStatus);
+    nsCOMPtr<nsIContentViewer> contentViewer = mContentViewer;
+    contentViewer->LoadComplete(aStatus);
     mIsExecutingOnLoadHandler = false;
 
     mEODForCurrentDocument = true;