Improve ClocklessAudioSink so it doesn't hog CPU if nothing to do.

media/audio/clockless_audio_sink.cc

 // Copyright 2013 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.
 
 #include "media/audio/clockless_audio_sink.h"
 
 #include "base/threading/simple_thread.h"
 #include "base/time/time.h"
 #include "media/base/audio_renderer_sink.h"
 
@@ skipping 18 matching lines @@
   // Generate a signal to stop calling Render().
   base::TimeDelta Stop() {
     stop_event_->Signal();
     thread_->Join();
     return playback_time_;
   }
 
  private:
    // Call Render() repeatedly, keeping track of the rendering time.
    virtual void Run() OVERRIDE {
-     base::TimeTicks start = base::TimeTicks::HighResNow();
+     base::TimeTicks start;
      while (!stop_event_->IsSignaled()) {
        int frames_received = callback_->Render(audio_bus_.get(), 0);
-       if (frames_received > 0) {
+       if (frames_received <= 0) {
+         // No data received, so let other threads run to provide data.
+         base::PlatformThread::YieldCurrentThread();
+       } else if (start.is_null()) {
+         // First time we processed some audio, so record the starting time.
+         start = base::TimeTicks::HighResNow();
+       } else {
          // Keep track of the last time data was rendered.
          playback_time_ = base::TimeTicks::HighResNow() - start;
        }
      }
    }
 
   AudioRendererSink::RenderCallback* callback_;
   scoped_ptr<AudioBus> audio_bus_;
   scoped_ptr<base::WaitableEvent> stop_event_;
   scoped_ptr<base::DelegateSimpleThread> thread_;
@@ skipping 39 matching lines @@
 void ClocklessAudioSink::Pause() {
   Stop();
 }
 
 bool ClocklessAudioSink::SetVolume(double volume) {
   // Audio is always muted.
   return volume == 0.0;
 }
 
 }  // namespace media