Have Frame::tree() return a reference

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 268 matching lines @@
 void InspectorDOMAgent::restore()
 {
     // Reset document to avoid early return from setDocument.
     m_document = 0;
     setDocument(m_pageAgent->mainFrame()->document());
 }
 
 Vector<Document*> InspectorDOMAgent::documents()
 {
     Vector<Document*> result;
-    for (Frame* frame = m_document->frame(); frame; frame = frame->tree()->traverseNext()) {
+    for (Frame* frame = m_document->frame(); frame; frame = frame->tree().traverseNext()) {
         Document* document = frame->document();
         if (!document)
             continue;
         result.append(document);
     }
     return result;
 }
 
 void InspectorDOMAgent::reset()
 {
@@ skipping 1717 matching lines @@
     if (!m_documentNodeToIdMap.contains(m_document)) {
         RefPtr<TypeBuilder::DOM::Node> root;
         getDocument(errorString, root);
         return errorString->isEmpty();
     }
     return true;
 }
 
 } // namespace WebCore