Cleans up gyp file for views example and removes duplicate code

ui/views/examples/message_box_example.h

 // Copyright (c) 2011 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_MESSAGE_BOX_EXAMPLE_H_
 #define UI_VIEWS_EXAMPLES_MESSAGE_BOX_EXAMPLE_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/examples/example_base.h"
 
 namespace views {
 class MessageBoxView;
 
 namespace examples {
 
 // A MessageBoxView example. This tests some of checkbox features as well.
-class MessageBoxExample : public ExampleBase, public ButtonListener {
+class VIEWS_EXAMPLES_EXPORT MessageBoxExample : public ExampleBase,
+                                                public ButtonListener {
  public:
   MessageBoxExample();
   virtual ~MessageBoxExample();
 
   // Overridden from ExampleBase:
   virtual void CreateExampleView(View* container) OVERRIDE;
 
  private:
   // Overridden from ButtonListener:
   virtual void ButtonPressed(Button* sender, const ui::Event& event) OVERRIDE;
 
   // The MessageBoxView to be tested.
   MessageBoxView* message_box_view_;
 
   // Control buttons to show the status and toggle checkbox in the
   // message box.
   Button* status_;
   Button* toggle_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageBoxExample);
 };
 
 }  // namespace examples
 }  // namespace views
 
 #endif  // UI_VIEWS_EXAMPLES_MESSAGE_BOX_EXAMPLE_H_