Allow creating non-thread-local Persistents that can be passed between threads.

Source/heap/HeapTest.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 266 matching lines @@
     void runThread()
     {
         ThreadState::attach();
 
         int gcCount = 0;
         while (!done()) {
             ThreadState::current()->safePoint(ThreadState::NoHeapPointersOnStack);
             {
                 IntWrapper* wrapper;
 
+                typedef Persistent<IntWrapper, GlobalPersistents> GlobalIntWrapperPersistent;
+                OwnPtr<GlobalIntWrapperPersistent> globalPersistent = adoptPtr(new GlobalIntWrapperPersistent(IntWrapper::create(0x0ed0cabb)));
+
                 for (int i = 0; i < numberOfAllocations; i++) {
                     wrapper = IntWrapper::create(0x0bbac0de);
-                    if (!(i % 10))
+                    if (!(i % 10)) {
+                        globalPersistent = adoptPtr(new GlobalIntWrapperPersistent(IntWrapper::create(0x0ed0cabb)));
                         ThreadState::current()->safePoint(ThreadState::HeapPointersOnStack);
+                    }
                     yield();
                 }
 
                 if (gcCount < gcPerThread) {
                     Heap::collectGarbage(ThreadState::HeapPointersOnStack);
                     gcCount++;
                     atomicIncrement(&m_gcCount);
                 }
 
                 EXPECT_EQ(wrapper->value(), 0x0bbac0de);
+                EXPECT_EQ((*globalPersistent)->value(), 0x0ed0cabb);
             }
             yield();
         }
         ThreadState::current()->cleanup();
         ThreadState::detach();
         atomicDecrement(&m_threadsToFinish);
     }
 
     volatile int m_gcCount;
     volatile int m_threadsToFinish;
@@ skipping 2000 matching lines @@
 DEFINE_GC_INFO(RefCountedAndGarbageCollected2);
 DEFINE_GC_INFO(SimpleFinalizedObject);
 DEFINE_GC_INFO(SimpleObject);
 DEFINE_GC_INFO(SuperClass);
 DEFINE_GC_INFO(SubData);
 DEFINE_GC_INFO(TestTypedHeapClass);
 DEFINE_GC_INFO(TraceCounter);
 DEFINE_GC_INFO(TransitionRefCounted);
 
 } // namespace