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

Source/core/accessibility/AXNodeObject.cpp

 /*
 * Copyright (C) 2012, Google Inc. All rights reserved.
 *
 * 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
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 1619 matching lines @@
     if (!document)
         return String();
 
     // Check if the HTML element has an aria-label for the webpage.
     if (Element* documentElement = document->documentElement()) {
         const AtomicString& ariaLabel = documentElement->getAttribute(aria_labelAttr);
         if (!ariaLabel.isEmpty())
             return ariaLabel;
     }
 
-    Node* owner = document->ownerElement();
-    if (owner) {
+    if (HTMLFrameOwnerElement* owner = document->ownerElement()) {
         if (isHTMLFrameElementBase(*owner)) {
-            const AtomicString& title = toElement(owner)->getAttribute(titleAttr);
+            const AtomicString& title = owner->getAttribute(titleAttr);
             if (!title.isEmpty())
                 return title;
-            return toElement(owner)->getNameAttribute();
         }
-        if (owner->isHTMLElement())
-            return toHTMLElement(owner)->getNameAttribute();
+        return owner->getNameAttribute();
     }
 
     String documentTitle = document->title();
     if (!documentTitle.isEmpty())
         return documentTitle;
 
-    owner = document->body();
-    if (owner && owner->isHTMLElement())
-        return toHTMLElement(owner)->getNameAttribute();
+    if (HTMLElement* body = document->body())
+        return body->getNameAttribute();
 
     return String();
 }
 
 void AXNodeObject::alternativeText(Vector<AccessibilityText>& textOrder) const
 {
     if (isWebArea()) {
         String webAreaText = alternativeTextForWebArea();
         if (!webAreaText.isEmpty())
             textOrder.append(AccessibilityText(webAreaText, AlternativeText));
@@ skipping 35 matching lines @@
     float range = maxValueForRange() - minValueForRange();
     float value = valueForRange();
 
     value += range * (percentChange / 100);
     setValue(String::number(value));
 
     axObjectCache()->postNotification(node(), AXObjectCache::AXValueChanged, true);
 }
 
 } // namespace blink