Virtual destructors should have virtual keyword.

chrome/browser/ui/gtk/notifications/balloon_view_host_gtk.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 CHROME_BROWSER_UI_GTK_NOTIFICATIONS_BALLOON_VIEW_HOST_GTK_H_
 #define CHROME_BROWSER_UI_GTK_NOTIFICATIONS_BALLOON_VIEW_HOST_GTK_H_
 #pragma once
 
 #include "chrome/browser/notifications/balloon_host.h"
 #include "ui/gfx/native_widget_types.h"
 
 class RenderWidgetHostViewGtk;
 
 // BalloonViewHost class is a delegate to the renderer host for the HTML
 // notification.  When initialized it creates a new RenderViewHost and loads
 // the contents of the toast into it.  It also handles links within the toast,
 // loading them into a new tab.
 class BalloonViewHost : public BalloonHost {
  public:
   explicit BalloonViewHost(Balloon* balloon);
 
-  ~BalloonViewHost() {
-    Shutdown();
-  }
+  virtual ~BalloonViewHost();
 
   // Changes the size of the balloon.
   void UpdateActualSize(const gfx::Size& new_size);
 
   // Accessors.
   gfx::NativeView native_view() const;
 
  protected:
   virtual void InitRenderWidgetHostView();
   virtual RenderWidgetHostView* render_widget_host_view() const;
 
  private:
   // The GTK-specific widget host view.  Owned by its native view.
   RenderWidgetHostViewGtk* render_widget_host_view_;
 
   DISALLOW_COPY_AND_ASSIGN(BalloonViewHost);
 };
 
 #endif  // CHROME_BROWSER_UI_GTK_NOTIFICATIONS_BALLOON_VIEW_HOST_GTK_H_