Use C++11 features in core/timing

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 291 matching lines @@
     DocumentLoadTiming* timing = documentLoadTiming();
     if (!timing)
         return 0;
 
     return monotonicTimeToIntegerMilliseconds(timing->loadEventEnd());
 }
 
 DocumentLoader* PerformanceTiming::documentLoader() const
 {
     if (!m_frame)
-        return 0;
+        return nullptr;
 
     return m_frame->loader().documentLoader();
 }
 
 const DocumentTiming* PerformanceTiming::documentTiming() const
 {
     if (!m_frame)
-        return 0;
+        return nullptr;
 
     Document* document = m_frame->document();
     if (!document)
-        return 0;
+        return nullptr;
 
     return &document->timing();
 }
 
 DocumentLoadTiming* PerformanceTiming::documentLoadTiming() const
 {
     DocumentLoader* loader = documentLoader();
     if (!loader)
-        return 0;
+        return nullptr;
 
     return loader->timing();
 }
 
 ResourceLoadTiming* PerformanceTiming::resourceLoadTiming() const
 {
     DocumentLoader* loader = documentLoader();
     if (!loader)
-        return 0;
+        return nullptr;
 
     return loader->response().resourceLoadTiming();
 }
 
 unsigned long long PerformanceTiming::monotonicTimeToIntegerMilliseconds(double monotonicSeconds) const
 {
     ASSERT(monotonicSeconds >= 0);
     const DocumentLoadTiming* timing = documentLoadTiming();
     if (!timing)
         return 0;
 
     return toIntegerMilliseconds(timing->monotonicTimeToPseudoWallTime(monotonicSeconds));
 }
 
 void PerformanceTiming::trace(Visitor* visitor)
 {
     DOMWindowProperty::trace(visitor);
 }
 
 } // namespace blink