Revert of mus: Rename .*PointerWatcher.* to .*PointerDownWatcher.*.

ash/common/pointer_down_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_DOWN_WATCHER_DELEGATE_H_
-#define ASH_COMMON_POINTER_DOWN_WATCHER_DELEGATE_H_
-
-#include "ash/ash_export.h"
-
-namespace views {
-class PointerDownWatcher;
-}
-
-namespace ash {
-
-// Allows different implementations of PointerDownWatcher in mus and
-// non-mus ash.
-class ASH_EXPORT PointerDownWatcherDelegate {
- public:
-  virtual ~PointerDownWatcherDelegate() {}
-
-  virtual void AddPointerDownWatcher(views::PointerDownWatcher* watcher) = 0;
-  virtual void RemovePointerDownWatcher(views::PointerDownWatcher* watcher) = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_COMMON_POINTER_DOWN_WATCHER_DELEGATE_H_