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

media/base/audio_capturer_source.h

 // Copyright (c) 2012 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.
 
 #ifndef MEDIA_BASE_AUDIO_CAPTURER_SOURCE_H_
 #define MEDIA_BASE_AUDIO_CAPTURER_SOURCE_H_
 
 #include <string>
 #include <vector>
 #include "base/memory/ref_counted.h"
 #include "media/base/audio_bus.h"
 #include "media/base/audio_parameters.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 // AudioCapturerSource is an interface representing the source for
 // captured audio.  An implementation will periodically call Capture() on a
 // callback object.
 class AudioCapturerSource
     : public base::RefCountedThreadSafe<media::AudioCapturerSource> {
  public:
   class CaptureCallback {
    public:
+    // Signals that audio recording has been started.  Called asynchronously
+    // after Start() has completed. If Start() encounters problems before this
+    // callback can be made, OnCaptureError will be called instead.
+    // This callback is provided for sources such as local audio sources that
+    // require asynchronous initialization so not all sources will support this
+    // notification.
+    virtual void OnCaptureStarted() {}
+
     // Callback to deliver the captured data from the OS.
     // TODO(chcunningham): Update delay argument to use frames instead of
     // milliseconds to prevent loss of precision. See http://crbug.com/587291.
     virtual void Capture(const AudioBus* audio_source,
                          int audio_delay_milliseconds,
                          double volume,
                          bool key_pressed) = 0;
 
     // Signals an error has occurred.
     virtual void OnCaptureError(const std::string& message) = 0;
@@ skipping 26 matching lines @@
   virtual void SetAutomaticGainControl(bool enable) = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<AudioCapturerSource>;
   virtual ~AudioCapturerSource() {}
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_CAPTURER_SOURCE_H_