Avoid heap allocation with uncoalesced touch events

content/browser/renderer_host/input/touch_event_queue.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 
 #include <deque>
 #include <map>
 
@@ skipping 142 matching lines @@
   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|.
+  // Ack all coalesced events in |acked_event| to the client with |ack_result|,
+  // updating the acked events with |optional_latency_info| if it exists.
   void AckTouchEventToClient(InputEventAckState ack_result,
-                             scoped_ptr<CoalescedWebTouchEvent> acked_event);
+                             scoped_ptr<CoalescedWebTouchEvent> acked_event,
+                             const ui::LatencyInfo* optional_latency_info);
 
   // 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,
@@ skipping 63 matching lines @@
   // setting for experimentation, but we may evolve it into an app-controlled
   // mode.
   const TouchScrollingMode touch_scrolling_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_