Introduce media::TimeSource.

media/base/wall_clock_time_source.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 MEDIA_BASE_WALL_CLOCK_TIME_SOURCE_H_
+#define MEDIA_BASE_WALL_CLOCK_TIME_SOURCE_H_
+
+#include "media/base/media_export.h"
+#include "media/base/time_source.h"
+
+namespace media {
+
+class MEDIA_EXPORT WallClockTimeSource : public TimeSource {
+ public:
+  WallClockTimeSource();
+  virtual ~WallClockTimeSource();
+
+  // TimeSource implementation.
+  virtual void StartTicking() OVERRIDE;
+  virtual void StopTicking() OVERRIDE;
+  virtual void SetPlaybackRate(float playback_rate) OVERRIDE;
+  virtual void SetMediaTimestamp(base::TimeDelta timestamp) OVERRIDE;
+  virtual base::TimeDelta CurrentMediaTimestamp() OVERRIDE;
+
+ private:
+  bool ticking_;
+  float playback_rate_;
+  base::TimeDelta base_timestamp_;
+  base::TimeTicks reference_wall_ticks_;

[xhwang, 2014/07/12 06:36:44]

Add comments for these variables. It's not obvious without looking at the impl.

[scherkus (not reviewing), 2014/07/17 23:52:56]

Done.

Let me know if this is what you had in mind.

+
+  DISALLOW_COPY_AND_ASSIGN(WallClockTimeSource);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_WALL_CLOCK_TIME_SOURCE_H_