Convert //ash from scoped_ptr to std::unique_ptr

ash/system/tray/default_system_tray_delegate.cc

 // 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.
 
 #include "ash/system/tray/default_system_tray_delegate.h"
 
 #include <string>
 #include <utility>
 
 #include "ash/networking_config_delegate.h"
@@ skipping 64 matching lines @@
 bool DefaultSystemTrayDelegate::GetBluetoothDiscovering() {
   return false;
 }
 
 VolumeControlDelegate* DefaultSystemTrayDelegate::GetVolumeControlDelegate()
     const {
   return volume_control_delegate_.get();
 }
 
 void DefaultSystemTrayDelegate::SetVolumeControlDelegate(
-    scoped_ptr<VolumeControlDelegate> delegate) {
+    std::unique_ptr<VolumeControlDelegate> delegate) {
   volume_control_delegate_ = std::move(delegate);
 }
 
 int DefaultSystemTrayDelegate::GetSystemTrayMenuWidth() {
   // This is the default width for English languages.
   return 300;
 }
 
 }  // namespace ash