Add a Clock and TickClock interface for mocking out time

media/base/clock.h

 // Copyright (c) 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 MEDIA_BASE_CLOCK_H_
 #define MEDIA_BASE_CLOCK_H_
 
 #include "base/basictypes.h"
 #include "base/time.h"
 #include "media/base/media_export.h"
 
+namespace base {
+class Clock;
+}  // namespace base
+
 namespace media {
 
 // A clock represents a single source of time to allow audio and video streams
 // to synchronize with each other.  Clock essentially tracks the media time with
 // respect to some other source of time, whether that may be the system clock or
 // updates via SetTime(). Clock uses linear interpolation to calculate the
 // current media time since the last time SetTime() was called.
 //
 // Clocks start off paused with a playback rate of 1.0f and a media time of 0.
 //
 // Clock is not thread-safe and must be externally locked.
 //
 // TODO(scherkus): Clock will some day be responsible for executing callbacks
 // given a media time.  This will be used primarily by video renderers.  For now
 // we'll keep using a poll-and-sleep solution.
 class MEDIA_EXPORT Clock {
  public:
-  // Type for a static function pointer that acts as a time source.
-  typedef base::Time(TimeProvider)();
-
-  explicit Clock(TimeProvider* time_provider);
+  explicit Clock(base::Clock* clock);
   ~Clock();
 
   // Returns true if the clock is running.
   bool IsPlaying() const;
 
   // Starts the clock and returns the current media time, which will increase
   // with respect to the current playback rate.
   base::TimeDelta Play();
 
   // Stops the clock and returns the current media time, which will remain
@@ skipping 41 matching lines @@
   void UpdateReferencePoints(base::TimeDelta current_time);
 
   // Returns the time elapsed based on the current reference points, ignoring
   // the |max_time_| cap.
   base::TimeDelta EstimatedElapsedTime();
 
   // Returns the current media time treating the given time as the latest
   // value as returned by |time_provider_|.
   base::TimeDelta ElapsedViaProvidedTime(const base::Time& time) const;
 
-  base::Time GetTimeFromProvider() const;
-
   base::TimeDelta ClampToValidTimeRange(base::TimeDelta time) const;
 
-  // Function returning current time in base::Time units.
-  TimeProvider* time_provider_;
+  base::Clock* const clock_;
 
   // Whether the clock is running.
   bool playing_;
 
   // Whether the clock is stalled because it has reached the |max_time_|
   // allowed.
   bool underflow_;
 
   // The system clock time when this clock last starting playing or had its
   // time set via SetTime().
@@ skipping 11 matching lines @@
 
   // Duration of the media.
   base::TimeDelta duration_;
 
   DISALLOW_COPY_AND_ASSIGN(Clock);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_CLOCK_H_