Make media::WallClockTimeSource thread safe.

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 "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
 #include "media/base/media_export.h"
 #include "media/base/time_source.h"
 
 namespace base {
 class TickClock;
 }
 
 namespace media {
 
 // A time source that uses interpolation based on the system clock.
 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 SetMediaTime(base::TimeDelta time) OVERRIDE;
   virtual base::TimeDelta CurrentMediaTime() OVERRIDE;
   virtual base::TimeDelta CurrentMediaTimeForSyncingVideo() OVERRIDE;
 
   void SetTickClockForTesting(scoped_ptr<base::TickClock> tick_clock);
 
  private:
+  base::TimeDelta CurrentMediaTime_Locked();
+
   scoped_ptr<base::TickClock> tick_clock_;
   bool ticking_;
 
   // While ticking we can interpolate the current media time by measuring the
   // delta between our reference ticks and the current system ticks and scaling
   // that time by the playback rate.
   float playback_rate_;
   base::TimeDelta base_time_;
   base::TimeTicks reference_wall_ticks_;
 
+  // TODO(scherkus): Remove internal locking from this class after access to
+  // Renderer::CurrentMediaTime() is single threaded http://crbug.com/370634
+  base::Lock lock_;
+
   DISALLOW_COPY_AND_ASSIGN(WallClockTimeSource);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_WALL_CLOCK_TIME_SOURCE_H_