Implement compositor thread VSync aligned event queue

ui/events/blink/compositor_thread_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 UI_EVENTS_BLINK_COMPOSITOR_THREAD_EVENT_QUEUE_H_
+#define UI_EVENTS_BLINK_COMPOSITOR_THREAD_EVENT_QUEUE_H_
+
+#include <deque>
+#include <memory>
+
+#include "ui/events/blink/event_with_callback.h"
+
+namespace ui {
+
+namespace test {
+class InputHandlerProxyEventQueueTest;
+}
+
+// CompositorThreadEventQueue is a coalescing queue. It will examine
+// the current events in the queue and will attempt to coalesce with
+// the last event.
+class CompositorThreadEventQueue {
+ public:
+  CompositorThreadEventQueue();
+  ~CompositorThreadEventQueue();
+
+  // Adds an event to the queue. The event may be coalesced with the last event.
+  void Queue(std::unique_ptr<EventWithCallback> event,
+             base::TimeTicks timestamp_now);
+
+  std::unique_ptr<EventWithCallback> Pop();
+
+  bool empty() const { return queue_.empty(); }
+
+  size_t size() const { return queue_.size(); }
+
+ private:
+  friend class test::InputHandlerProxyEventQueueTest;
+  using EventQueue = std::deque<std::unique_ptr<EventWithCallback>>;
+  EventQueue queue_;
+
+  DISALLOW_COPY_AND_ASSIGN(CompositorThreadEventQueue);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_BLINK_COMPOSITOR_THREAD_EVENT_QUEUE_H_