Add ShellDelegate, MediaDelegate and KeyboardUI stubs to mus ash

ash/common/pointer_watcher_delegate.h

 // Copyright 2016 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_COMMON_POINTER_WATCHER_DELEGATE_H_
+#define ASH_COMMON_POINTER_WATCHER_DELEGATE_H_
+
 #include "ash/ash_export.h"
 
 namespace views {
 class PointerWatcher;
 }
 
 namespace ash {
 
 // Allows different implementations of PointerWatcher in mus and non-mus ash.
 class ASH_EXPORT PointerWatcherDelegate {
  public:
   virtual ~PointerWatcherDelegate() {}
 
   virtual void AddPointerWatcher(views::PointerWatcher* watcher) = 0;
   virtual void RemovePointerWatcher(views::PointerWatcher* watcher) = 0;
 };
 
 }  // namespace ash
+
+#endif  // ASH_COMMON_POINTER_WATCHER_DELEGATE_H_