NOT READY FOR REVIEW - switch to a subscriber model for rendering stats

cc/rendering_stats_subscriber.h

Index: cc/rendering_stats_subscriber.h
diff --git a/cc/rendering_stats_subscriber.h b/cc/rendering_stats_subscriber.h
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+++ b/cc/rendering_stats_subscriber.h
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+// Copyright 2012 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 rendering_stats_subscriber_h
+#define rendering_stats_subscriber_h
+
+#include "base/memory/scoped_ptr.h"
+#include "base/time.h"
+
+#include <vector>
+
+namespace cc {
+
+class RenderingStatsSubscriber {
+public:
+  static scoped_ptr<RenderingStatsSubscriber> create();
+
+  virtual ~RenderingStatsSubscriber();
+
+  // Will have functions here to inform the subscriber of the goings on in the
+  // compositor.
+  void markBeginningOfFrame(base::TimeTicks timestamp);
+
+  void handledScrollEvent(bool content_did_move);
+
+  void getFPSAndStandardDeviation(double& average_fps,
+                                  double& standard_deviation) const;
+
+private:
+  RenderingStatsSubscriber();
+
+  std::vector<base::TimeTicks> time_stamp_history_;
+  bool is_scrolling_;
+  bool has_scrolled_;
+};
+
+}  // namespace cc
+
+#endif // rendering_stats_subscriber_h