Fix start/stop of html5 audio stream and race condition when pausing.

content/renderer/media/webrtc_audio_device_impl.cc

Index: content/renderer/media/webrtc_audio_device_impl.cc
===================================================================
--- content/renderer/media/webrtc_audio_device_impl.cc	(revision 113847)
+++ content/renderer/media/webrtc_audio_device_impl.cc	(working copy)
@@ -59,7 +59,7 @@
   return ret;
 }
 
-void WebRtcAudioDeviceImpl::Render(
+size_t WebRtcAudioDeviceImpl::Render(
     const std::vector<float*>& audio_data,
     size_t number_of_frames,
     size_t audio_delay_milliseconds) {
@@ -111,6 +111,7 @@
         bytes_per_sample_,
         number_of_frames);
   }
+  return number_of_frames;
 }
 
 void WebRtcAudioDeviceImpl::Capture(