Enable the volume slider in Ash for windows.

ash/system/audio/tray_audio_delegate.h

 // Copyright 2014 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 ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_
 #define ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_
 
 namespace ash {
 namespace system {
 
-class TrayAudioDelegate {
+class ASH_EXPORT TrayAudioDelegate {
  public:
 
   enum { kNoAudioDeviceIcon = -1 };
 
   virtual ~TrayAudioDelegate() {}
 
   // Sets the volume level of the output device to the minimum level which is
   // deemed to be audible.
   virtual void AdjustOutputVolumeToAudibleLevel() = 0;
 
@@ skipping 17 matching lines @@
   virtual void SetOutputAudioIsMuted(bool is_muted) = 0;
 
   // Sets the volume level of the output device in the range 0%-100%
   virtual void SetOutputVolumeLevel(int level) = 0;
 };
 
 }  // namespace system
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_