Ignore fullscreen requests for the current fullscreen element

Source/core/dom/Fullscreen.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
@@ skipping 189 matching lines @@
 
     return true;
 }
 
 void Fullscreen::requestFullscreen(Element& element, RequestType requestType)
 {
     // Ignore this request if the document is not in a live frame.
     if (!document()->isActive())
         return;
 
+    // If |element| is on top of |doc|'s fullscreen element stack, terminate these substeps.
+    if (&element == fullscreenElement())
+        return;
+
     do {
         // 1. If any of the following conditions are true, terminate these steps and queue a task to fire
         // an event named fullscreenerror with its bubbles attribute set to true on the context object's
         // node document:
 
         // The fullscreen element ready check returns false.
         if (!elementReady(element, requestType))
             break;
 
         // This algorithm is not allowed to show a pop-up:
@@ skipping 380 matching lines @@
 void Fullscreen::trace(Visitor* visitor)
 {
     visitor->trace(m_fullScreenElement);
     visitor->trace(m_fullScreenElementStack);
     visitor->trace(m_fullScreenRenderer);
     visitor->trace(m_eventQueue);
     DocumentSupplement::trace(visitor);
 }
 
 } // namespace blink