Implement Wheel Gesture Scrolling on OSX.

content/browser/renderer_host/input/mouse_wheel_event_queue.h

 // Copyright 2016 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_MOUSE_WHEEL_EVENT_QUEUE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_MOUSE_WHEEL_EVENT_QUEUE_H_
 
 #include <deque>
 
 #include "base/time/time.h"
 #include "content/browser/renderer_host/event_with_latency_info.h"
 #include "content/common/content_export.h"
 #include "content/common/input/input_event_ack_state.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 
 namespace content {
 
 // The duration in which a ScrollEnd will be sent after the last
 // ScrollUpdate was sent for wheel based gesture scrolls.
-const int64_t kDefaultWheelScrollTransactionMs = 100;
+// Set the default wheel transaction to 0ms until
+// crbug.com/526463 is fully implemented.
+const int64_t kDefaultWheelScrollTransactionMs = 0;  // 100;
 
 class QueuedWebMouseWheelEvent;
 
 // Interface with which MouseWheelEventQueue can forward mouse wheel events,
 // and dispatch mouse wheel event responses.
 class CONTENT_EXPORT MouseWheelEventQueueClient {
  public:
   virtual ~MouseWheelEventQueueClient() {}
 
   virtual void SendMouseWheelEventImmediately(
@@ skipping 38 matching lines @@
     return !wheel_queue_.empty() || event_sent_for_gesture_ack_;
   }
 
   size_t queued_size() const { return wheel_queue_.size(); }
   bool event_in_flight() const {
     return event_sent_for_gesture_ack_ != nullptr;
   }
 
  private:
   void TryForwardNextEventToRenderer();
-  void SendScrollEnd(blink::WebGestureEvent update_event);
-  void SendGesture(const GestureEventWithLatencyInfo& gesture);
+  void SendScrollEnd(blink::WebGestureEvent update_event, bool synthetic);
+  void SendScrollBegin(const GestureEventWithLatencyInfo& gesture_update,
+                       bool synthetic);
 
   MouseWheelEventQueueClient* client_;
-  bool needs_scroll_begin_;
   base::OneShotTimer scroll_end_timer_;
 
   typedef std::deque<QueuedWebMouseWheelEvent*> WheelEventQueue;
   WheelEventQueue wheel_queue_;
   scoped_ptr<QueuedWebMouseWheelEvent> event_sent_for_gesture_ack_;
+
+  // True if a non-synthetic GSB needs to be sent before a GSU is sent.
+  bool needs_scroll_begin_;
+
+  // True if a non-synthetic GSE needs to be sent because a non-synthetic
+  // GSB has been sent in the past.
+  bool needs_scroll_end_;
+
   bool send_gestures_;
   int64_t scroll_transaction_ms_;
   blink::WebGestureDevice scrolling_device_;
 
   DISALLOW_COPY_AND_ASSIGN(MouseWheelEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_MOUSE_WHEEL_EVENT_QUEUE_H_