Cleans up gyp file for views example and removes duplicate code

ui/views/controls/combobox/combobox_listener.h

Index: ui/views/controls/combobox/combobox_listener.h
diff --git a/ui/views/controls/combobox/combobox_listener.h b/ui/views/controls/combobox/combobox_listener.h
index 2609f647023f8ce1381d189671db8cdf596c65bd..faa41df89e4a113e97e461a0b1953dcc0f9078e5 100644
--- a/ui/views/controls/combobox/combobox_listener.h
+++ b/ui/views/controls/combobox/combobox_listener.h
@@ -5,13 +5,15 @@
 #ifndef UI_VIEWS_CONTROLS_COMBOBOX_COMBOBOX_LISTENER_H_
 #define UI_VIEWS_CONTROLS_COMBOBOX_COMBOBOX_LISTENER_H_
 
+#include "ui/views/views_export.h"
+
 namespace views {
 
 class Combobox;
 
 // An interface implemented by an object to let it know that the selected index
 // has changed.
-class ComboboxListener {
+class VIEWS_EXPORT ComboboxListener {
  public:
   virtual void OnSelectedIndexChanged(Combobox* combobox) = 0;