Expose performance.memory in workers

Source/core/timing/Performance.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel 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.
@@ skipping 56 matching lines @@
 
 ExecutionContext* Performance::executionContext() const
 {
     if (!frame())
         return 0;
     return frame()->document();
 }
 
 PassRefPtr<MemoryInfo> Performance::memory() const
 {
-    return MemoryInfo::create(m_frame);
+    return MemoryInfo::create(executionContext());
 }
 
 PerformanceNavigation* Performance::navigation() const
 {
     if (!m_navigation)
         m_navigation = PerformanceNavigation::create(m_frame);
 
     return m_navigation.get();
 }
 
@@ skipping 183 matching lines @@
         m_userTiming = UserTiming::create(this);
     m_userTiming->clearMeasures(measureName);
 }
 
 double Performance::now() const
 {
     return 1000.0 * (monotonicallyIncreasingTime() - m_referenceTime);
 }
 
 } // namespace WebCore