Refactoring the way begin frame sources inside scheduler work.

cc/output/vsync_parameter_observer.h

+// Copyright 2014 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_OUTPUT_VSYNC_PARAMETER_OBSERVER_H_
+#define CC_OUTPUT_VSYNC_PARAMETER_OBSERVER_H_
+
+#include "base/time/time.h"
+
+// Interface for a class which observes the parameters regarding vsync
+// information.
+class VSyncParameterObserver {
+ public:
+  virtual void OnUpdateVSyncParameters(base::TimeTicks timebase,
+                                       base::TimeDelta interval) = 0;
+};
+
+#endif  // CC_OUTPUT_VSYNC_PARAMETER_OBSERVER_H_