Add the "virtual" keyword on method overrides that are missing it.

chrome/renderer/media/audio_renderer_impl.h

Index: chrome/renderer/media/audio_renderer_impl.h
diff --git a/chrome/renderer/media/audio_renderer_impl.h b/chrome/renderer/media/audio_renderer_impl.h
index 7c0ea8ed2bcf4b9f2cf9053d9792d15ffea9ec00..5c8d4cc295adec7775d5c4c84ee775cdf588050d 100644
--- a/chrome/renderer/media/audio_renderer_impl.h
+++ b/chrome/renderer/media/audio_renderer_impl.h
@@ -61,13 +61,13 @@ class AudioRendererImpl : public media::AudioRendererBase,
 
   // Methods called on IO thread ----------------------------------------------
   // AudioMessageFilter::Delegate methods, called by AudioMessageFilter.
-  void OnRequestPacket(AudioBuffersState buffers_state);
-  void OnStateChanged(const ViewMsg_AudioStreamState_Params& state);
-  void OnCreated(base::SharedMemoryHandle handle, uint32 length);
-  void OnLowLatencyCreated(base::SharedMemoryHandle handle,
-                           base::SyncSocket::Handle socket_handle,
-                           uint32 length);
-  void OnVolume(double volume);
+  virtual void OnRequestPacket(AudioBuffersState buffers_state);
+  virtual void OnStateChanged(const ViewMsg_AudioStreamState_Params& state);
+  virtual void OnCreated(base::SharedMemoryHandle handle, uint32 length);
+  virtual void OnLowLatencyCreated(base::SharedMemoryHandle handle,
+                                   base::SyncSocket::Handle socket_handle,
+                                   uint32 length);
+  virtual void OnVolume(double volume);
 
   // Methods called on pipeline thread ----------------------------------------
   // media::Filter implementation.