views: Factor out Listener from Combobox into its own header file.

views/controls/combobox/combobox.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 VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_
 #define VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_
 #pragma once
 
 #include <string>
 
 #include "ui/gfx/native_widget_types.h"
 #include "views/controls/combobox/native_combobox_wrapper.h"
 #include "views/view.h"
 
 namespace ui {
 class ComboboxModel;
 }
 
 namespace views {
 
+class ComboboxListener;
+
 // A non-editable combo-box (aka a drop-down list)
 class VIEWS_EXPORT Combobox : public View {
  public:
   // The combobox's class name.
   static const char kViewClassName[];
 
-  class Listener {
-   public:
-    // This is invoked once the selected item changed.
-    virtual void ItemChanged(Combobox* combo_box,
-                             int prev_index,
-                             int new_index) = 0;
-
-   protected:
-    virtual ~Listener() {}
-  };
-
   // |model| is not owned by the combo box.
   explicit Combobox(ui::ComboboxModel* model);
   virtual ~Combobox();
 
   // Register |listener| for item change events.
-  void set_listener(Listener* listener) {
+  void set_listener(ComboboxListener* listener) {
     listener_ = listener;
   }
 
   // Inform the combo box that its model changed.
   void ModelChanged();
 
   // Gets/Sets the selected item.
   int selected_item() const { return selected_item_; }
   void SetSelectedItem(int index);
 
@@ skipping 33 matching lines @@
                                     View* child) OVERRIDE;
   virtual std::string GetClassName() const OVERRIDE;
 
   // The object that actually implements the native combobox.
   NativeComboboxWrapper* native_wrapper_;
 
  private:
   // Our model.
   ui::ComboboxModel* model_;
 
-  // Item change listener.
-  Listener* listener_;
+  // The combobox's listener. Notified when the selected item change.
+  ComboboxListener* listener_;
 
   // The current selection.
   int selected_item_;
 
   // The accessible name of the text field.
   string16 accessible_name_;
 
   DISALLOW_COPY_AND_ASSIGN(Combobox);
 };
 
 }  // namespace views
 
 #endif  // VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_