Use mojo volume interfaces for mash and classic ash.

ash/common/system/tray/default_system_tray_delegate.h

Index: ash/common/system/tray/default_system_tray_delegate.h
diff --git a/ash/common/system/tray/default_system_tray_delegate.h b/ash/common/system/tray/default_system_tray_delegate.h
index 5536c352b6df3902b727401c86e711ede85bb98e..a4550ff71d125fa6d9bad42885ed140f0165d356 100644
--- a/ash/common/system/tray/default_system_tray_delegate.h
+++ b/ash/common/system/tray/default_system_tray_delegate.h
@@ -5,8 +5,6 @@
 #ifndef ASH_COMMON_SYSTEM_TRAY_DEFAULT_SYSTEM_TRAY_DELEGATE_H_
 #define ASH_COMMON_SYSTEM_TRAY_DEFAULT_SYSTEM_TRAY_DELEGATE_H_
 
-#include <memory>
-
 #include "ash/ash_export.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
 #include "base/macros.h"
@@ -29,14 +27,10 @@ class ASH_EXPORT DefaultSystemTrayDelegate : public SystemTrayDelegate {
   bool GetBluetoothAvailable() override;
   bool GetBluetoothEnabled() override;
   bool GetBluetoothDiscovering() override;
-  VolumeControlDelegate* GetVolumeControlDelegate() const override;
-  void SetVolumeControlDelegate(
-      std::unique_ptr<VolumeControlDelegate> delegate) override;
   int GetSystemTrayMenuWidth() override;
 
  private:
   bool bluetooth_enabled_;
-  std::unique_ptr<VolumeControlDelegate> volume_control_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultSystemTrayDelegate);
 };