Warn on missing OVERRIDE/virtual everywhere, not just in header files.

chrome/browser/extensions/api/audio/audio_service.cc

Index: chrome/browser/extensions/api/audio/audio_service.cc
diff --git a/chrome/browser/extensions/api/audio/audio_service.cc b/chrome/browser/extensions/api/audio/audio_service.cc
index 3406f65cd4c4afdd61872d0395088d3a6356a2fb..e5fa3dbd87c53d9adadc9e1dc299d3b2cb7a20ab 100644
--- a/chrome/browser/extensions/api/audio/audio_service.cc
+++ b/chrome/browser/extensions/api/audio/audio_service.cc
@@ -12,11 +12,11 @@ class AudioServiceImpl : public AudioService {
   virtual ~AudioServiceImpl() {}
 
   // Called by listeners to this service to add/remove themselves as observers.
-  virtual void AddObserver(Observer* observer);
-  virtual void RemoveObserver(Observer* observer);
+  virtual void AddObserver(Observer* observer) OVERRIDE;
+  virtual void RemoveObserver(Observer* observer) OVERRIDE;
 
   // Start to query audio device information.
-  virtual void StartGetInfo(const GetInfoCallback& callback);
+  virtual void StartGetInfo(const GetInfoCallback& callback) OVERRIDE;
 };
 
 void AudioServiceImpl::AddObserver(Observer* observer) {