Have Document::timing() / Document::contextFeatures() return a reference

Source/core/timing/PerformanceTiming.cpp

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 306 matching lines @@
 
 const DocumentTiming* PerformanceTiming::documentTiming() const
 {
     if (!m_frame)
         return 0;
 
     Document* document = m_frame->document();
     if (!document)
         return 0;
 
-    return document->timing();
+    return &document->timing();
 }
 
 DocumentLoadTiming* PerformanceTiming::documentLoadTiming() const
 {
     DocumentLoader* loader = documentLoader();
     if (!loader)
         return 0;
 
     return loader->timing();
 }
@@ skipping 11 matching lines @@
 {
     ASSERT(monotonicSeconds >= 0);
     const DocumentLoadTiming* timing = documentLoadTiming();
     if (!timing)
         return 0;
 
     return toIntegerMilliseconds(timing->monotonicTimeToPseudoWallTime(monotonicSeconds));
 }
 
 } // namespace WebCore