Add the SharedWorker.workerStart property for high resolution timers.

Source/modules/performance/WorkerGlobalScopePerformance.cpp

 /*
  * Copyright (C) 2013 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 44 matching lines @@
     WorkerGlobalScopePerformance* supplement = static_cast<WorkerGlobalScopePerformance*>(WorkerSupplement::from(context, supplementName()));
     if (!supplement) {
         supplement = new WorkerGlobalScopePerformance();
         provideTo(context, supplementName(), adoptPtr(supplement));
     }
     return supplement;
 }
 
 WorkerPerformance* WorkerGlobalScopePerformance::performance(WorkerGlobalScope* context)
 {
-    return from(context)->getPerformance(context);
+    return from(context)->performance();
 }
 
-WorkerPerformance* WorkerGlobalScopePerformance::getPerformance(WorkerGlobalScope* context)
+WorkerPerformance* WorkerGlobalScopePerformance::performance()
 {
     if (!m_performance)
-        m_performance = WorkerPerformance::create(context);
+        m_performance = WorkerPerformance::create();
     return m_performance.get();
 }
 
 } // namespace WebCore