Bug 1053766 - Use the statechange notification blocker to avoid some transient notifications. r=botond

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1309,7 +1309,10 @@ nsEventStatus AsyncPanZoomController::OnTouchEnd(const MultiTouchInput& aEvent)
     mX.SetVelocity(0);
     mY.SetVelocity(0);
     // Clear our state so that we don't stay in the PANNING state
-    // if DispatchFling() gives the fling to somone else.
+    // if DispatchFling() gives the fling to somone else. However,
+    // don't send the state change notification until we've determined
+    // what our final state is to avoid notification churn.
+    StateChangeNotificationBlocker blocker(this);
     SetState(NOTHING);
     APZC_LOG("%p starting a fling animation\n", this);
     // Make a local copy of the tree manager pointer and check that it's not
@@ -2468,6 +2471,11 @@ bool AsyncPanZoomController::AdvanceAnimations(const TimeStamp& aSampleTime)
 {
   AssertOnCompositorThread();
 
+  // Don't send any state-change notifications until the end of the function,
+  // because we may go through some intermediate states while we finish
+  // animations and start new ones.
+  StateChangeNotificationBlocker blocker(this);
+
   // The eventual return value of this function. The compositor needs to know
   // whether or not to advance by a frame as soon as it can. For example, if a
   // fling is happening, it has to keep compositing so that the animation is