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

Source/core/dom/Document.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, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 1924 matching lines @@
 
     ScriptForbiddenScope forbidScript;
 
     RefPtr<FrameView> frameView = view();
     if (frameView && frameView->isInPerformLayout()) {
         // View layout should not be re-entrant.
         ASSERT_NOT_REACHED();
         return;
     }
 
-    if (Element* oe = ownerElement())
-        oe->document().updateLayout();
+    if (HTMLFrameOwnerElement* owner = ownerElement())
+        owner->document().updateLayout();
 
     updateRenderTreeIfNeeded();
 
     if (!isActive())
         return;
 
     if (frameView->needsLayout())
         frameView->layout();
 
     if (lifecycle().state() < DocumentLifecycle::LayoutClean)
@@ skipping 2537 matching lines @@
     if (!parent || !parent->isLocalFrame())
         return 0;
     return toLocalFrame(parent)->document();
 }
 
 Document& Document::topDocument() const
 {
     // FIXME: Not clear what topDocument() should do in the OOPI case--should it return the topmost
     // available Document, or something else?
     Document* doc = const_cast<Document*>(this);
-    for (Element* element = doc->ownerElement(); element; element = doc->ownerElement())
+    for (HTMLFrameOwnerElement* element = doc->ownerElement(); element; element = doc->ownerElement())
         doc = &element->document();
 
     ASSERT(doc);
     return *doc;
 }
 
 WeakPtrWillBeRawPtr<Document> Document::contextDocument()
 {
     if (m_contextDocument)
         return m_contextDocument;
@@ skipping 1280 matching lines @@
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (WeakDocumentSet::const_iterator it = set.begin(); it != set.end(); ++it) {
         fprintf(stderr, "- Document %p URL: %s\n", *it, (*it)->url().string().utf8().data());
     }
 }
 #endif