Add undeclared virtual destructors part 2...

views/controls/button/button.h

 // Copyright (c) 2010 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_BUTTON_BUTTON_H_
 #define VIEWS_CONTROLS_BUTTON_BUTTON_H_
 
 #include "views/view.h"
 
 namespace views {
 
 class Button;
 class Event;
 
 // An interface implemented by an object to let it know that a button was
 // pressed.
 class ButtonListener {
  public:
   virtual void ButtonPressed(Button* sender, const views::Event& event) = 0;
+
+ protected:
+  virtual ~ButtonListener() {}
 };
 
 // A View representing a button. Depending on the specific type, the button
 // could be implemented by a native control or custom rendered.
 class Button : public View {
  public:
   virtual ~Button();
 
   void SetTooltipText(const std::wstring& tooltip_text);
 
@@ skipping 34 matching lines @@
 
   // Event flags present when the button was clicked.
   int mouse_event_flags_;
 
   DISALLOW_COPY_AND_ASSIGN(Button);
 };
 
 }  // namespace views
 
 #endif  // VIEWS_CONTROLS_BUTTON_BUTTON_H_