bug 1270916 - switch to use the new mutation event queue system r=davidb

This puts events in the queue instead of the event tree, and then fires them
based on the queue.  Some tests need to be adjusted to make sure they check
constraints on event order correctly.

accessible/base/NotificationController.cpp

@@ -802,9 +802,9 @@ NotificationController::WillRefresh(mozilla::TimeStamp aTime)
   // events causes script to run.
   mObservingState = eRefreshProcessing;
 
-  RefPtr<DocAccessible> deathGrip(mDocument);
-  mEventTree.Process(deathGrip);
-  deathGrip = nullptr;
+  CoalesceMutationEvents();
+  ProcessMutationEvents();
+  mEventGeneration = 0;
 
   // Now that we are done with them get rid of the events we fired.
   RefPtr<AccTreeMutationEvent> mutEvent = Move(mFirstMutationEvent);