ui: Cleanup class/struct forward declarations

ui/aura/mus/window_mus.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 UI_AURA_MUS_WINDOW_MUS_H_
 #define UI_AURA_MUS_WINDOW_MUS_H_
 
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "services/ui/public/interfaces/cursor.mojom.h"
 #include "ui/aura/aura_export.h"
 #include "ui/aura/mus/mus_types.h"
 
 namespace gfx {
 class Rect;
-class Vector2d;
 }
 
 namespace ui {
 namespace mojom {
 enum class OrderDirection;
 }
 }
 
 namespace aura {
 
@@ skipping 76 matching lines @@
 
   void set_server_id(Id id) { server_id_ = id; }
 
   Id server_id_ = kInvalidServerId;
   const WindowMusType window_mus_type_;
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_MUS_H_