Have Frame::tree() return a reference

Source/core/dom/TreeScope.cpp

 /*
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  * Copyright (C) 2012 Apple 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 328 matching lines @@
     ASSERT(node);
     ASSERT(!node->isDocumentNode());
     ASSERT_WITH_SECURITY_IMPLICATION(!node->m_deletionHasBegun);
     TreeScopeAdopter adopter(node, this);
     if (adopter.needsScopeChange())
         adopter.execute();
 }
 
 static Element* focusedFrameOwnerElement(Frame* focusedFrame, Frame* currentFrame)
 {
-    for (; focusedFrame; focusedFrame = focusedFrame->tree()->parent()) {
-        if (focusedFrame->tree()->parent() == currentFrame)
+    for (; focusedFrame; focusedFrame = focusedFrame->tree().parent()) {
+        if (focusedFrame->tree().parent() == currentFrame)
             return focusedFrame->ownerElement();
     }
     return 0;
 }
 
 Element* TreeScope::adjustedFocusedElement()
 {
     Document& document = rootNode()->document();
     Element* element = document.focusedElement();
     if (!element && document.page())
@@ skipping 130 matching lines @@
             result = element;
         for (ShadowRoot* shadowRoot = element->youngestShadowRoot(); shadowRoot; shadowRoot = shadowRoot->olderShadowRoot()) {
             if (Element* shadowResult = shadowRoot->getElementByAccessKey(key))
                 result = shadowResult;
         }
     }
     return result;
 }
 
 } // namespace WebCore