Use LocalMediaStreamAudioSource for screen-casting use cases.

content/renderer/media/webrtc/processed_local_audio_source.cc

Index: content/renderer/media/webrtc/processed_local_audio_source.cc
diff --git a/content/renderer/media/webrtc/processed_local_audio_source.cc b/content/renderer/media/webrtc/processed_local_audio_source.cc
index b25469372a3625d563595da73736689b78ec2e44..c2a13553f9942e007cae0ed42d914148ceaa63b5 100644
--- a/content/renderer/media/webrtc/processed_local_audio_source.cc
+++ b/content/renderer/media/webrtc/processed_local_audio_source.cc
@@ -350,6 +350,7 @@ int ProcessedLocalAudioSource::GetBufferSize(int sample_rate) const {
   DCHECK(thread_checker_.CalledOnValidThread());
 #if defined(OS_ANDROID)
   // TODO(henrika): Re-evaluate whether to use same logic as other platforms.
+  // http://crbug.com/638081
   return (2 * sample_rate / 100);
 #endif
 
@@ -367,7 +368,7 @@ int ProcessedLocalAudioSource::GetBufferSize(int sample_rate) const {
   // fall-back.
   //
   // TODO(miu): Identify where/why the buffer size might be missing, fix the
-  // code, and then require it here.
+  // code, and then require it here. http://crbug.com/638081
   return (sample_rate / 100);
 }