Fix playback rate w/o audio. Remove unused SetPlaybackRate().

content/renderer/media/render_audiosourceprovider.cc

Index: content/renderer/media/render_audiosourceprovider.cc
diff --git a/content/renderer/media/render_audiosourceprovider.cc b/content/renderer/media/render_audiosourceprovider.cc
index d450d9d5c893ae6485edfa37f4fb97ef9c54c4b3..a1051e0e5d2b3df8ede8693c993fda0d7ca9e38e 100644
--- a/content/renderer/media/render_audiosourceprovider.cc
+++ b/content/renderer/media/render_audiosourceprovider.cc
@@ -115,12 +115,6 @@ void RenderAudioSourceProvider::Pause(bool flush) {
   is_running_ = false;
 }
 
-void RenderAudioSourceProvider::SetPlaybackRate(float rate) {
-  base::AutoLock auto_lock(sink_lock_);
-  if (!client_)
-    default_sink_->SetPlaybackRate(rate);
-}
-
 bool RenderAudioSourceProvider::SetVolume(double volume) {
   base::AutoLock auto_lock(sink_lock_);
   if (!client_)