Handle mac trackpad zoom via GesturePinch events

content/browser/renderer_host/input/gesture_event_queue.h

 // Copyright 2014 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_GESTURE_EVENT_QUEUE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_GESTURE_EVENT_QUEUE_H_
 
 #include <deque>
 
 #include "base/basictypes.h"
@@ skipping 50 matching lines @@
 // http://crbug.com/148443.
 class CONTENT_EXPORT GestureEventQueue {
  public:
   // Both |client| and |touchpad_client| must outlive the GestureEventQueue.
   GestureEventQueue(GestureEventQueueClient* client,
                      TouchpadTapSuppressionControllerClient* touchpad_client);
   ~GestureEventQueue();
 
   // Returns |true| if the caller should immediately forward the provided
   // |GestureEventWithLatencyInfo| argument to the renderer.
+  // If this function returns false, then the event may be queued and forwared
+  // at a later point.
   bool ShouldForward(const GestureEventWithLatencyInfo&);

[jdduke (slow), 2014/03/26 23:13:43]

I've had a refactoring patch, for the longest time, that changes this to
|QueueEvent()|... this |ShouldForward| business is just confusing.

[Rick Byers, 2014/03/27 01:44:09]

Yeah, I get confused by this every time and have to keep reminding myself about
it.  Cleaning this up sounds great!  

 
   // Indicates that the caller has received an acknowledgement from the renderer
   // with state |ack_result| and event |type|. May send events if the queue is
   // not empty.
   void ProcessGestureAck(InputEventAckState ack_result,
                          blink::WebInputEvent::Type type,
                          const ui::LatencyInfo& latency);
 
   // Sets the state of the |fling_in_progress_| field to indicate that a fling
   // is definitely not in progress.
@@ skipping 135 matching lines @@
   // Whether scroll-ending events should be deferred when a scroll is active.
   // Defaults to true.
   bool debounce_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_GESTURE_EVENT_QUEUE_H_