Measure requestFullscreen() replacing the pending element

third_party/WebKit/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)
@@ skipping 463 matching lines @@
         continue;
       }
 
       // 4. Otherwise, do nothing for this document. It stays the same.
     } while (++current != docs.end());
 
     from(document).m_forCrossProcessDescendant = forCrossProcessDescendant;
 
     // 5. Return, and run the remaining steps asynchronously.
     // 6. Optionally, perform some animation.
+    if (from(document).m_pendingFullscreenElement) {
+      UseCounter::count(document,
+                        UseCounter::FullscreenRequestWithPendingElement);
+    }
     from(document).m_pendingFullscreenElement = &element;
     document.frame()->chromeClient().enterFullscreen(*document.frame());
 
     // 7. Optionally, display a message indicating how the user can exit
     // displaying the context object fullscreen.
     return;
   } while (false);
 
   from(document).enqueueErrorEvent(element, requestType);
 }
@@ skipping 369 matching lines @@
 DEFINE_TRACE(Fullscreen) {
   visitor->trace(m_pendingFullscreenElement);
   visitor->trace(m_fullscreenElementStack);
   visitor->trace(m_currentFullScreenElement);
   visitor->trace(m_eventQueue);
   Supplement<Document>::trace(visitor);
   ContextLifecycleObserver::trace(visitor);
 }
 
 }  // namespace blink