Implement async touchmove dispatch during scroll

content/browser/renderer_host/input/touch_event_queue.h

Index: content/browser/renderer_host/input/touch_event_queue.h
diff --git a/content/browser/renderer_host/input/touch_event_queue.h b/content/browser/renderer_host/input/touch_event_queue.h
index 03d3210adb429c2fb3a9cebe33215f3058eb97c8..5d2edc27ec660cc1af0d986086cdc96e680c5d83 100644
--- a/content/browser/renderer_host/input/touch_event_queue.h
+++ b/content/browser/renderer_host/input/touch_event_queue.h
@@ -48,12 +48,11 @@ class CONTENT_EXPORT TouchEventQueue {
     // using the disposition to determine whether a scroll update should be
     // sent.  Mobile Safari's default overflow scroll behavior.
     TOUCH_SCROLLING_MODE_SYNC_TOUCHMOVE,
-    // Like sync, except that consumed scroll events cause subsequent touchmove
-    // events to be suppressed.  Unconsumed scroll events return touchmove
-    // events to being dispatched synchronously (so scrolling may be hijacked
-    // when a scroll limit is reached, and later resumed). http://goo.gl/RShsdN
-    TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE,
-    TOUCH_SCROLLING_MODE_DEFAULT = TOUCH_SCROLLING_MODE_TOUCHCANCEL
+    // Send touchmove events throughout a scroll, but throttle sending and
+    // ignore the ACK as long as scrolling remains possible.  Unconsumed scroll
+    // events return touchmove events to being dispatched synchronously.
+    TOUCH_SCROLLING_MODE_ASYNC_TOUCHMOVE,
+    TOUCH_SCROLLING_MODE_DEFAULT = TOUCH_SCROLLING_MODE_ASYNC_TOUCHMOVE
   };
 
   // The |client| must outlive the TouchEventQueue. If
@@ -120,7 +119,7 @@ class CONTENT_EXPORT TouchEventQueue {
   friend class TouchTimeoutHandler;
   friend class TouchEventQueueTest;
 
-  bool HasTimeoutEvent() const;
+  bool HasPendingAsyncTouchMoveForTesting() const;
   bool IsTimeoutRunningForTesting() const;
   const TouchEventWithLatencyInfo& GetLatestEventForTesting() const;
 
@@ -128,16 +127,32 @@ class CONTENT_EXPORT TouchEventQueue {
   // events being sent to the renderer.
   void FlushQueue();
 
-  // Walks the queue, checking each event for |ShouldForwardToRenderer()|.
-  // If true, forwards the touch event and stops processing further events.
-  // If false, acks the event with |INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS|.
+  // Walks the queue, checking each event with |FilterBeforeForwarding()|.
+  // If allowed, forwards the touch event and stops processing further events.
+  // Otherwise, acks the event with |INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS|.
   void TryForwardNextEventToRenderer();
 
-  // Pops the touch-event from the top of the queue and sends it to the
-  // TouchEventQueueClient. This reduces the size of the queue by one.
+  // Forwards the event at the head of the queue to the renderer.
+  void ForwardNextEventToRenderer();
+
+  // Pops the touch-event from the head of the queue and acks it to the client.
+  void PopTouchEventToClient(InputEventAckState ack_result);
+
+  // Pops the touch-event from the top of the queue and acks it to the client,
+  // updating the event with |renderer_latency_info|.
   void PopTouchEventToClient(InputEventAckState ack_result,
                              const ui::LatencyInfo& renderer_latency_info);
 
+  // Ack all coalesced events in |acked_event| to the client with |ack_result|.
+  void AckTouchEventToClient(InputEventAckState ack_result,
+                             scoped_ptr<CoalescedWebTouchEvent> acked_event);
+
+  // Safely pop the head of the queue.
+  scoped_ptr<CoalescedWebTouchEvent> PopTouchEvent();
+
+  // Dispatch |touch| to the client.
+  void SendTouchEventImmediately(const TouchEventWithLatencyInfo& touch);
+
   enum PreFilterResult {
     ACK_WITH_NO_CONSUMER_EXISTS,
     ACK_WITH_NOT_CONSUMED,
@@ -161,10 +176,14 @@ class CONTENT_EXPORT TouchEventQueue {
   typedef std::map<int, InputEventAckState> TouchPointAckStates;
   TouchPointAckStates touch_ack_states_;
 
+  // Position of the first touch in the most recent sequence forwarded to the
+  // client.
+  gfx::PointF touch_sequence_start_position_;
+
   // Used to defer touch forwarding when ack dispatch triggers |QueueEvent()|.
   // If not NULL, |dispatching_touch_ack_| is the touch event of which the ack
   // is being dispatched.
-  CoalescedWebTouchEvent* dispatching_touch_ack_;
+  const CoalescedWebTouchEvent* dispatching_touch_ack_;
 
   // Used to prevent touch timeout scheduling if we receive a synchronous
   // ack after forwarding a touch event to the client.
@@ -188,12 +207,15 @@ class CONTENT_EXPORT TouchEventQueue {
   // been preventDefaulted.
   scoped_ptr<TouchMoveSlopSuppressor> touchmove_slop_suppressor_;
 
-  // Whether touchmove events should be dropped due to the
-  // TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE mode.  Note that we can't use
-  // touch_filtering_state_ for this (without adding a few new states and
-  // complicating the code significantly) because it can occur with and without
-  // timeout, and shouldn't cause touchend to be dropped.
-  bool absorbing_touch_moves_;
+  // Whether touch events should remain buffered and dispatched asynchronously
+  // while a scroll sequence is active.  In this mode, touchmove's are throttled
+  // and ack'ed immediately, but remain buffered in |pending_async_touch_move_|
+  // until a sufficient time period has elapsed since the last sent touch event.
+  // For details see the design doc at http://goo.gl/lVyJAa.
+  bool send_touch_events_async_;
+  scoped_ptr<TouchEventWithLatencyInfo> pending_async_touch_move_;
+  double last_sent_touch_timestamp_sec_;
+  bool needs_async_touch_move_for_outer_slop_region_;
 
   // How touch events are handled during scrolling.  For now this is a global
   // setting for experimentation, but we may evolve it into an app-controlled