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

media/audio/clockless_audio_sink.cc

Index: media/audio/clockless_audio_sink.cc
diff --git a/media/audio/clockless_audio_sink.cc b/media/audio/clockless_audio_sink.cc
index ab56115c27fefe5304dff4d506b257fedc4cc945..ff809d0541dd49fc87f6559bf901563cb5c92cdc 100644
--- a/media/audio/clockless_audio_sink.cc
+++ b/media/audio/clockless_audio_sink.cc
@@ -36,10 +36,16 @@ class ClocklessAudioSinkThread : public base::DelegateSimpleThread::Delegate {
  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;
        }