Fix GCC build for target 'all'

ui/views/examples/examples_window.h

 // Copyright (c) 2012 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_VIEWS_EXAMPLES_EXAMPLES_WINDOW_H_
 #define UI_VIEWS_EXAMPLES_EXAMPLES_WINDOW_H_
 
 #include <memory>
 #include <vector>
 
 #include "ui/gfx/native_widget_types.h"
+#include "ui/views/examples/example_base.h"
 #include "ui/views/examples/views_examples_export.h"
 
 namespace views {
 namespace examples {
 
-class ExampleBase;
-
 enum Operation {
   DO_NOTHING_ON_CLOSE = 0,
   QUIT_ON_CLOSE,
 };
 
 // Shows a window with the views examples in it. |extra_examples| contains any
 // additional examples to add. |window_context| is used to determine where the
 // window should be created (see |Widget::InitParams::context| for details).
 VIEWS_EXAMPLES_EXPORT void ShowExamplesWindow(
     Operation operation,
     gfx::NativeWindow window_context = nullptr,
     std::vector<std::unique_ptr<ExampleBase>> extra_examples =
         std::vector<std::unique_ptr<ExampleBase>>());
 
 }  // namespace examples
 }  // namespace views
 
 #endif  // UI_VIEWS_EXAMPLES_EXAMPLES_WINDOW_H_