Offer User Timing in workers

Source/modules/performance/WorkerPerformance.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 20 matching lines @@
 #include "config.h"
 #include "modules/performance/WorkerPerformance.h"
 
 #include "core/timing/MemoryInfo.h"
 #include "core/workers/DedicatedWorkerGlobalScope.h"
 #include "core/workers/WorkerGlobalScope.h"
 #include "wtf/CurrentTime.h"
 
 namespace blink {
 
-WorkerPerformance::WorkerPerformance()
+WorkerPerformance::WorkerPerformance(WorkerGlobalScope* context)
+    : PerformanceBase(context->timeOrigin())
+    , ContextLifecycleObserver(context)
 {
 }
 
+ExecutionContext* WorkerPerformance::executionContext() const
+{
+    return ContextLifecycleObserver::executionContext();
+}
+
 DEFINE_TRACE(WorkerPerformance)
 {
     visitor->trace(m_memoryInfo);
-}
-
-double WorkerPerformance::now(ExecutionContext* context) const
-{
-    ASSERT(context);
-    ASSERT(context->isWorkerGlobalScope());
-    WorkerGlobalScope* workerGlobalScope = toWorkerGlobalScope(context);
-    return 1000.0 * (monotonicallyIncreasingTime() - workerGlobalScope->timeOrigin());
+    PerformanceBase::trace(visitor);
+    ContextLifecycleObserver::trace(visitor);
 }
 
 MemoryInfo* WorkerPerformance::memory()
 {
     if (!m_memoryInfo)
         m_memoryInfo = MemoryInfo::create();
 
     return m_memoryInfo.get();
 }
 
 } // namespace blink