Add the SharedWorker.workerStart property for high resolution timers.

Source/modules/performance/WorkerPerformance.h

 /*
  * 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 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef WorkerPerformance_h
 #define WorkerPerformance_h
 
+#include "bindings/v8/ScriptWrappable.h"
 #include "core/dom/ContextLifecycleObserver.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 
 namespace WebCore {
 
 class ExecutionContext;
 
-class WorkerPerformance : public RefCounted<WorkerPerformance>, public ContextLifecycleObserver {
+class WorkerPerformance : public ScriptWrappable, public RefCounted<WorkerPerformance> {
 public:
-    static PassRefPtr<WorkerPerformance> create(ExecutionContext* context) { return adoptRef(new WorkerPerformance(context)); }
+    static PassRefPtr<WorkerPerformance> create() { return adoptRef(new WorkerPerformance()); }
     ~WorkerPerformance();
 
-    double now() const;
+    double now(ExecutionContext*) const;
 
 private:
-    explicit WorkerPerformance(ExecutionContext*);
+    WorkerPerformance();
 };
 
 }
 
 #endif // WorkerPerformance_h