views::LabelButton should not call virtual methods from its constructor

ui/views/controls/button/blue_button.h

 // Copyright 2013 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_CONTROLS_BUTTON_BLUE_BUTTON_H_
 #define UI_VIEWS_CONTROLS_BUTTON_BLUE_BUTTON_H_
 
 #include "base/compiler_specific.h"
 #include "ui/views/controls/button/label_button.h"
 
 namespace views {
 
-// A class representing a blue button.
-class VIEWS_EXPORT BlueButton : public LabelButton {
+// A class representing a blue button. Declared final because the constructor
+// calls virtual methods.
+class VIEWS_EXPORT BlueButton final : public LabelButton {
  public:
   static const char kViewClassName[];
 
+  // Constructs a BlueButton and initializes with LabelButton::InitAsButton().
   BlueButton(ButtonListener* listener, const base::string16& text);
+
   ~BlueButton() override;
 
  private:
   // Overridden from LabelButton:
   void ResetColorsFromNativeTheme() override;
   const char* GetClassName() const override;
   scoped_ptr<LabelButtonBorder> CreateDefaultBorder() const override;
 
   DISALLOW_COPY_AND_ASSIGN(BlueButton);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_BUTTON_BLUE_BUTTON_H_