ui: Cleanup class/struct forward declarations

ui/aura/test/mus/test_window_tree_client_setup.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_TEST_MUS_TEST_WINDOW_TREE_CLIENT_SETUP_H_
 #define UI_AURA_TEST_MUS_TEST_WINDOW_TREE_CLIENT_SETUP_H_
 
 #include <memory>
 
 #include "base/macros.h"
 
-namespace display {
-class Display;
-}
-
 namespace aura {
 
 class TestWindowTree;
 class WindowManagerDelegate;
 class WindowTreeClient;
 class WindowTreeClientDelegate;
 
 // TestWindowTreeClientSetup is used to create a WindowTreeClient that is not
 // connected to mus.
 class TestWindowTreeClientSetup {
@@ skipping 22 matching lines @@
   std::unique_ptr<TestWindowTree> window_tree_;
 
   std::unique_ptr<WindowTreeClient> window_tree_client_;
 
   DISALLOW_COPY_AND_ASSIGN(TestWindowTreeClientSetup);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_TEST_MUS_TEST_WINDOW_TREE_CLIENT_SETUP_H_