Notifications: Retain button hover state during content updates.

ui/message_center/views/notification_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_MESSAGE_CENTER_VIEWS_NOTIFICATION_BUTTON_H_
 #define UI_MESSAGE_CENTER_VIEWS_NOTIFICATION_BUTTON_H_
 
 #include "ui/gfx/image/image_skia.h"
 #include "ui/views/controls/button/custom_button.h"
 #include "ui/views/painter.h"
@@ skipping 14 matching lines @@
 
   void SetIcon(const gfx::ImageSkia& icon);
   void SetTitle(const base::string16& title);
 
   // Overridden from views::View:
   virtual gfx::Size GetPreferredSize() OVERRIDE;
   virtual int GetHeightForWidth(int width) OVERRIDE;
   virtual void OnPaint(gfx::Canvas* canvas) OVERRIDE;
   virtual void OnFocus() OVERRIDE;
   virtual void OnBlur() OVERRIDE;
+  virtual void ViewHierarchyChanged(
+      const ViewHierarchyChangedDetails& details) OVERRIDE;
 
   // Overridden from views::CustomButton:
   virtual void StateChanged() OVERRIDE;
 
  private:
   views::ImageView* icon_;
   views::Label* title_;
   scoped_ptr<views::Painter> focus_painter_;
 
   DISALLOW_COPY_AND_ASSIGN(NotificationButton);
 };
 
 }  // namespace message_center
 
 #endif // UI_MESSAGE_CENTER_VIEWS_NOTIFICATION_BUTTON_H_