Add a new GetInstance() method for remaining files with singleton classes under chrome/browser.

chrome/browser/chromeos/audio_handler.h

Index: chrome/browser/chromeos/audio_handler.h
diff --git a/chrome/browser/chromeos/audio_handler.h b/chrome/browser/chromeos/audio_handler.h
index 67addcbf3146a046b64462bb5e4a4c7de6122b2a..721ce79a5866853a865b4a07d583446521b0f4a4 100644
--- a/chrome/browser/chromeos/audio_handler.h
+++ b/chrome/browser/chromeos/audio_handler.h
@@ -15,9 +15,7 @@ class PulseAudioMixer;
 
 class AudioHandler {
  public:
-  static AudioHandler* instance() {
-    return Singleton<AudioHandler>::get();
-  }
+  static AudioHandler* instance();
 
   // Get volume level in our internal 0-100% range, 0 being pure silence.
   // Volume may go above 100% if another process changes PulseAudio's volume.