Add a new audio extension event OnLevelChanged.

chrome/browser/ui/ash/system_tray_delegate_chromeos.h

Index: chrome/browser/ui/ash/system_tray_delegate_chromeos.h
diff --git a/chrome/browser/ui/ash/system_tray_delegate_chromeos.h b/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
index b250503f8757549f8de9e191d4850833d17c2029..e07bb8475f65fcad77772c8cf95270839b6f6b88 100644
--- a/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
+++ b/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
@@ -215,9 +215,9 @@ class SystemTrayDelegateChromeOS
       ui::ime::InputMethodMenuManager* manager) override;
 
   // Overridden from CrasAudioHandler::AudioObserver.
-  void OnOutputVolumeChanged() override;
+  void OnOutputNodeVolumeChanged(uint64_t node_id, int volume) override;
   void OnOutputMuteChanged() override;
-  void OnInputGainChanged() override;
+  void OnInputNodeGainChanged(uint64_t node_id, int gain) override;
   void OnInputMuteChanged() override;
   void OnAudioNodesChanged() override;
   void OnActiveOutputNodeChanged() override;