Use tighter typing for Document::ownerElement() return value

Source/core/inspector/InspectorDOMAgent.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
@@ skipping 1813 matching lines @@
         return;
 
     // Re-push document once it is loaded.
     discardFrontendBindings();
     if (enabled())
         m_frontend->documentUpdated();
 }
 
 void InspectorDOMAgent::invalidateFrameOwnerElement(LocalFrame* frame)
 {
-    Element* frameOwner = frame->document()->ownerElement();
+    HTMLFrameOwnerElement* frameOwner = frame->document()->ownerElement();
     if (!frameOwner)
         return;
 
     int frameOwnerId = m_documentNodeToIdMap->get(frameOwner);
     if (!frameOwnerId)
         return;
 
     // Re-add frame owner element together with its new children.
     int parentId = m_documentNodeToIdMap->get(innerParentNode(frameOwner));
     m_frontend->childNodeRemoved(parentId, frameOwnerId);
@@ skipping 350 matching lines @@
     visitor->trace(m_searchResults);
 #endif
     visitor->trace(m_history);
     visitor->trace(m_domEditor);
     visitor->trace(m_listener);
     InspectorBaseAgent::trace(visitor);
 }
 
 } // namespace blink