Fix getUserMedia so that failure is reported for invalid audio sources.

chrome/renderer/media/cast_receiver_audio_valve.cc

 // Copyright 2015 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 "chrome/renderer/media/cast_receiver_audio_valve.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "media/base/audio_parameters.h"
 
@@ skipping 38 matching lines @@
     // TimeTicks::Now() is being called after the |lock_| was acquired in order
     // to provide the most accurate delay value.
     const int audio_delay_milliseconds =
         (base::TimeTicks::Now() - playout_time).InMilliseconds();
 
     cb_->Capture(&audio_bus, audio_delay_milliseconds, 1.0 /* volume */,
                  false /* key_pressed */);
   }
 }
 
+void CastReceiverAudioValve::OnStarted() {
+  base::AutoLock lock(lock_);
+  if (cb_)
+    cb_->OnCaptureStarted();
+}
+
 void CastReceiverAudioValve::Stop() {
   base::AutoLock lock(lock_);
   cb_ = nullptr;
 }