Link things together and enable the device selection for linux and mac.

content/renderer/media/audio_input_device.h

Index: content/renderer/media/audio_input_device.h
diff --git a/content/renderer/media/audio_input_device.h b/content/renderer/media/audio_input_device.h
index c766cda953fcf1b07f7a27d2cf7051b2dfd93728..afe76b9dc8beffba1a1dc2010cd681cd609de8a8 100644
--- a/content/renderer/media/audio_input_device.h
+++ b/content/renderer/media/audio_input_device.h
@@ -100,9 +100,10 @@ class CONTENT_EXPORT AudioInputDevice
 
   class CONTENT_EXPORT CaptureEventHandler {
    public:
-    // Notification to the client that the device with the specific index has
-    // been started. This callback is triggered as a result of StartDevice().
-    virtual void OnDeviceStarted(int device_index) = 0;
+    // Notification to the client that the device with the specific |device_id|
+    // has been started.
+    // This callback is triggered as a result of StartDevice().
+    virtual void OnDeviceStarted(const std::string& device_id) = 0;
 
     // Notification to the client that the device has been stopped.
     virtual void OnDeviceStopped() = 0;
@@ -151,7 +152,7 @@ class CONTENT_EXPORT AudioInputDevice
                                    uint32 length);
   virtual void OnVolume(double volume);
   virtual void OnStateChanged(AudioStreamState state);
-  virtual void OnDeviceReady(int index);
+  virtual void OnDeviceReady(const std::string& device_id);
 
  private:
   // Methods called on IO thread ----------------------------------------------