Coalesce async touch move events until the ack back from render

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 a61b90d8eca8c1707d31b3e9bfbadabb175047a0..a40dbb6d367f6baa825fa1f3178c379136b87095 100644
--- a/content/browser/renderer_host/input/touch_event_queue.h
+++ b/content/browser/renderer_host/input/touch_event_queue.h
@@ -66,6 +66,8 @@ class CONTENT_EXPORT TouchEventQueue {
   void ProcessTouchAck(InputEventAckState ack_result,
                        const ui::LatencyInfo& latency_info);
 
+  void ProcessUncancelableTouchMoveAck();
+
   // When GestureScrollBegin is received, we send a touch cancel to renderer,
   // route all the following touch events directly to client, and ignore the
   // ack for the touch cancel. When Gesture{ScrollEnd,FlingStart} is received,
@@ -102,6 +104,14 @@ class CONTENT_EXPORT TouchEventQueue {
 
   bool has_handlers() const { return has_handlers_; }
 
+  int PendingUncancelableEventAckCount() const {
+    return pending_uncancelable_event_ack_count_;
+  }
+
+  int SentUncancelableTouchMoveCount() const {
+    return sent_uncancelable_touch_move_count_;
+  }
+
  private:
   class TouchTimeoutHandler;
   class TouchMoveSlopSuppressor;
@@ -202,6 +212,18 @@ class CONTENT_EXPORT TouchEventQueue {
   // For details see the design doc at http://goo.gl/lVyJAa.
   bool send_touch_events_async_;
   scoped_ptr<TouchEventWithLatencyInfo> pending_async_touchmove_;
+
+  // Once this value is greater than 0, which means we should ignore the
+  // following ignore_ack_ numbers of acks from render for async touch moves.
+  int pending_uncancelable_event_ack_count_;
+
+  // For uncancelable touch moves, not only we send a fake ack, but also a real
+  // ack from render, which we use to decide when to send the next touch move.
+  // This can help avoid the touch event queue keep growing when render handles
+  // touchmove slow. We use sent_uncancelable_touch_move_count_ to count the
+  // number of uncancelable touch moves sent out are waiting for
+  // their acks back from render.
+  int sent_uncancelable_touch_move_count_;

[tdresser, 2015/03/25 14:16:18]

I'm still not clear on why we need both pending_uncancelable_event_ack_count_
and sent_uncancelable_touch_move_count_.

Let's talk it over in person.

   double last_sent_touch_timestamp_sec_;
 
   // Event is saved to compare pointer positions for new touchmove events.