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

chrome/renderer/media/audio_renderer_impl.h

 // Copyright (c) 2010 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.
 //
 // Audio rendering unit utilizing audio output stream provided by browser
 // process through IPC.
 //
 // Relationship of classes.
 //
 //    AudioRendererHost                AudioRendererImpl
@@ skipping 43 matching lines @@
 class AudioRendererImpl : public media::AudioRendererBase,
                           public AudioMessageFilter::Delegate,
                           public MessageLoop::DestructionObserver {
  public:
   // Methods called on Render thread ------------------------------------------
   explicit AudioRendererImpl(AudioMessageFilter* filter);
   virtual ~AudioRendererImpl();
 
   // 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.
   virtual void SetPlaybackRate(float rate);
   virtual void Pause(media::FilterCallback* callback);
   virtual void Seek(base::TimeDelta time, media::FilterCallback* callback);
   virtual void Play(media::FilterCallback* callback);
 
   // media::AudioRenderer implementation.
   virtual void SetVolume(float volume);
@@ skipping 67 matching lines @@
   // State variables for prerolling.
   bool prerolling_;
 
   // Remaining bytes for prerolling to complete.
   uint32 preroll_bytes_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererImpl);
 };
 
 #endif  // CHROME_RENDERER_MEDIA_AUDIO_RENDERER_IMPL_H_