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

content/browser/web_contents/web_contents_view_aura.cc

 // 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.
 
 #include "content/browser/web_contents/web_contents_view_aura.h"
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/metrics/histogram.h"
@@ skipping 1560 matching lines @@
   web_contents_->GetRenderViewHost()->DragTargetDrop(
       event.location(),
       gfx::Screen::GetScreenFor(GetNativeView())->GetCursorScreenPoint(),
       ConvertAuraEventFlagsToWebInputEventModifiers(event.flags()));
   if (drag_dest_delegate_)
     drag_dest_delegate_->OnDrop();
   current_drop_data_.reset();
   return ConvertFromWeb(current_drag_op_);
 }
 
-void WebContentsViewAura::OnWindowParentChanged(aura::Window* window,
-                                                aura::Window* parent) {
-  // Ignore any visibility changes in the hierarchy below.
-  if (window != window_.get() && window_->Contains(window))
-    return;
-
-  // On Windows we will get called with a parent of NULL as part of the shut
-  // down process. As such we do only change the visibility when a parent gets
-  // set.
-  if (parent)
-    UpdateWebContentsVisibility(window->IsVisible());
-}
-
 void WebContentsViewAura::OnWindowVisibilityChanged(aura::Window* window,
                                                     bool visible) {
   // Ignore any visibility changes in the hierarchy below.
   if (window != window_.get() && window_->Contains(window))
     return;
 
   UpdateWebContentsVisibility(visible);
 }
 
 void WebContentsViewAura::UpdateWebContentsVisibility(bool visible) {
@@ skipping 13 matching lines @@
   if (visible) {
     if (!web_contents_->should_normally_be_visible())
       web_contents_->WasShown();
   } else {
     if (web_contents_->should_normally_be_visible())
       web_contents_->WasHidden();
   }
 }
 
 }  // namespace content