Make DocumentLoader::timing return a reference

Source/modules/performance/SharedWorkerPerformance.cpp

 /*
  * Copyright (c) 2014, Opera Software ASA. 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 53 matching lines @@
 }
 
 double SharedWorkerPerformance::getWorkerStart(ExecutionContext* context, SharedWorker&) const
 {
     ASSERT(context);
     ASSERT(context->isDocument());
     Document* document = toDocument(context);
     if (!document->loader())
         return 0;
 
-    double navigationStart = document->loader()->timing()->navigationStart();
+    double navigationStart = document->loader()->timing().navigationStart();
     return m_timeOrigin - navigationStart;
 }
 
 } // namespace blink