Add a new audio extension event OnLevelChanged.

chrome/browser/ui/ash/system_tray_delegate_chromeos.h

 // Copyright 2013 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.
 
 #ifndef CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_DELEGATE_CHROMEOS_H_
 #define CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_DELEGATE_CHROMEOS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 197 matching lines @@
 
   // Overridden from InputMethodManager::Observer.
   void InputMethodChanged(input_method::InputMethodManager* manager,
                           bool show_message) override;
 
   // Overridden from InputMethodMenuManager::Observer.
   void InputMethodMenuItemChanged(
       ui::ime::InputMethodMenuManager* manager) override;
 
   // Overridden from CrasAudioHandler::AudioObserver.
-  void OnOutputVolumeChanged() override;
+  void OnOutputNodeVolumeChanged(uint64 node_id, double volume) override;
   void OnOutputMuteChanged() override;
   void OnInputGainChanged() override;
   void OnInputMuteChanged() override;
   void OnAudioNodesChanged() override;
   void OnActiveOutputNodeChanged() override;
   void OnActiveInputNodeChanged() override;
 
   // Overridden from BluetoothAdapter::Observer.
   void AdapterPresentChanged(device::BluetoothAdapter* adapter,
                              bool present) override;
@@ skipping 72 matching lines @@
 
   base::WeakPtrFactory<SystemTrayDelegateChromeOS> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayDelegateChromeOS);
 };
 
 ash::SystemTrayDelegate* CreateSystemTrayDelegate();
 
 }  // namespace chromeos
 #endif  // CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_DELEGATE_CHROMEOS_H_