Implement compositor thread VSync aligned event queue

ui/events/blink/compositor_thread_event_queue.cc

+// 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.
+
+#include "ui/events/blink/compositor_thread_event_queue.h"
+
+namespace ui {
+
+CompositorThreadEventQueue::CompositorThreadEventQueue() {}
+
+CompositorThreadEventQueue::~CompositorThreadEventQueue() {}
+
+void CompositorThreadEventQueue::Queue(
+    std::unique_ptr<EventWithCallback> event) {
+  if (!queue_.empty() && queue_.back()->CanCoalesceWith(*event)) {

[tdresser, 2016/11/01 18:12:44]

This doesn't handle the scroll/pinch/scroll case, does it?

[chongz, 2016/11/02 21:29:32]

No it doesn't. I've filed https://crbug.com/661601 for this improvement. Can I
add support in the next CL or do you want me to do it now?

[tdresser, 2016/11/04 16:51:03]

Next CL is fine.

+    queue_.back()->CoalesceWith(event.get());
+    return;
+  }
+
+  queue_.emplace_back(std::move(event));
+}
+
+std::unique_ptr<EventWithCallback> CompositorThreadEventQueue::Pop() {
+  std::unique_ptr<EventWithCallback> result;
+  if (!queue_.empty()) {
+    result.reset(queue_.front().release());
+    queue_.pop_front();
+  }
+  return result;
+}
+
+}  // namespace ui