Use mojo volume interfaces for mash and classic ash.

ash/common/system/tray/default_system_tray_delegate.cc

Index: ash/common/system/tray/default_system_tray_delegate.cc
diff --git a/ash/common/system/tray/default_system_tray_delegate.cc b/ash/common/system/tray/default_system_tray_delegate.cc
index 102832b441a6859d3b1f1900e9919e56dd5272de..f58c2141d32010c7b2ff868b3197a748d29cba2e 100644
--- a/ash/common/system/tray/default_system_tray_delegate.cc
+++ b/ash/common/system/tray/default_system_tray_delegate.cc
@@ -8,7 +8,6 @@
 #include <utility>
 
 #include "ash/common/system/networking_config_delegate.h"
-#include "ash/common/system/volume_control_delegate.h"
 #include "base/message_loop/message_loop.h"
 #include "base/time/time.h"
 
@@ -64,16 +63,6 @@ bool DefaultSystemTrayDelegate::GetBluetoothDiscovering() {
   return false;
 }
 
-VolumeControlDelegate* DefaultSystemTrayDelegate::GetVolumeControlDelegate()
-    const {
-  return volume_control_delegate_.get();
-}
-
-void DefaultSystemTrayDelegate::SetVolumeControlDelegate(
-    std::unique_ptr<VolumeControlDelegate> delegate) {
-  volume_control_delegate_ = std::move(delegate);
-}
-
 int DefaultSystemTrayDelegate::GetSystemTrayMenuWidth() {
   // This is the default width for English languages.
   return 300;