ash: Cleanup class/struct forward declarations

ash/mus/test/wm_test_base.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_MUS_TEST_WM_TEST_BASE_H_
 #define ASH_MUS_TEST_WM_TEST_BASE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 11 matching lines @@
 }
 
 namespace ui {
 class Window;
 }
 
 namespace ash {
 namespace mus {
 
 class AshTestImplMus;
-class RootWindowController;
 class WmTestHelper;
 
 // Base class for window manager tests that want to configure
 // WindowTreeClient without a client to mus.
 class WmTestBase : public testing::Test {
  public:
   WmTestBase();
   ~WmTestBase() override;
 
   // TODO(sky): temporary until http://crbug.com/611563 is fixed.
@@ skipping 38 matching lines @@
   bool teardown_called_ = false;
   std::unique_ptr<WmTestHelper> test_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(WmTestBase);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_TEST_WM_TEST_BASE_H_