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() {}
+
+// TODO(chongz): Support coalescing events across interleaved boundaries.
+// https://crbug.com/661601
+void CompositorThreadEventQueue::Queue(std::unique_ptr<EventWithCallback> event,
+                                       base::TimeTicks timestamp_now) {
+  if (!queue_.empty() && queue_.back()->CanCoalesceWith(*event)) {
+    queue_.back()->CoalesceWith(event.get(), timestamp_now);
+    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