When we switch tabs in chrome, the tab being switched away from gets hidden/shown/hidden.

content/browser/web_contents/web_contents_view_aura.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_AURA_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_AURA_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 160 matching lines @@
   virtual void OnKeyEvent(ui::KeyEvent* event) OVERRIDE;
   virtual void OnMouseEvent(ui::MouseEvent* event) OVERRIDE;
 
   // Overridden from aura::client::DragDropDelegate:
   virtual void OnDragEntered(const ui::DropTargetEvent& event) OVERRIDE;
   virtual int OnDragUpdated(const ui::DropTargetEvent& event) OVERRIDE;
   virtual void OnDragExited() OVERRIDE;
   virtual int OnPerformDrop(const ui::DropTargetEvent& event) OVERRIDE;
 
   // Overridden from aura::WindowObserver:
-  virtual void OnWindowParentChanged(aura::Window* window,
-                                     aura::Window* parent) OVERRIDE;
   virtual void OnWindowVisibilityChanged(aura::Window* window,
                                          bool visible) OVERRIDE;
 
   // Update the web contents visiblity.
   void UpdateWebContentsVisibility(bool visible);
 
   scoped_ptr<aura::Window> window_;
 
   // The window that shows the screenshot of the history page during an
   // overscroll navigation gesture.
@@ skipping 39 matching lines @@
   // On Windows we can run into problems if resources get released within the
   // initialization phase while the content (and its dimensions) are not known.
   bool is_or_was_visible_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsViewAura);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_AURA_H_