Cleans up gyp file for views example and removes duplicate code

ui/views/examples/slider_example.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_SLIDER_EXAMPLE_H_
 #define UI_VIEWS_EXAMPLES_SLIDER_EXAMPLE_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/views/controls/slider.h"
 #include "ui/views/examples/example_base.h"
 
 namespace views {
 class Label;
 
 namespace examples {
 
-class SliderExample : public ExampleBase, public SliderListener {
+class VIEWS_EXAMPLES_EXPORT SliderExample : public ExampleBase,
+                                            public SliderListener {
  public:
   SliderExample();
   virtual ~SliderExample();
 
   // Overridden from ExampleBase:
   virtual void CreateExampleView(View* container) OVERRIDE;
 
  private:
   // Overridden from SliderListener:
   virtual void SliderValueChanged(Slider* sender,
                                   float value,
                                   float old_value,
                                   SliderChangeReason reason) OVERRIDE;
 
   Slider* slider_;
   Label* label_;
 
   DISALLOW_COPY_AND_ASSIGN(SliderExample);
 };
 
 }  // namespace examples
 }  // namespace views
 
 #endif  // UI_VIEWS_EXAMPLES_SLIDER_EXAMPLE_H_