Decouple BrowserCompositorOutputSurface from BeginFrameSource.

cc/scheduler/vsync_observer.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 CC_SCHEDULER_VSYNC_OBSERVER_H_
+#define CC_SCHEDULER_VSYNC_OBSERVER_H_
+
+#include "base/time/time.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+class CC_EXPORT VSyncObserver {
+ public:
+  virtual void OnUpdateVSyncParameters(base::TimeTicks timebase,
+                                       base::TimeDelta interval) = 0;
+};
+
+}  // namespace cc
+
+#endif  // CC_SCHEDULER_VSYNC_OBSERVER_H_