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

Source/heap/HeapTest.cpp

Index: Source/heap/HeapTest.cpp
diff --git a/Source/heap/HeapTest.cpp b/Source/heap/HeapTest.cpp
index c7f3b758084821592ab9b7e1a0acc99ff6d58ef1..597c050f00cb5418eaf17b178eaaa1b5ac8014b4 100644
--- a/Source/heap/HeapTest.cpp
+++ b/Source/heap/HeapTest.cpp
@@ -284,10 +284,15 @@ private:
             {
                 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();
                 }
 
@@ -298,6 +303,7 @@ private:
                 }
 
                 EXPECT_EQ(wrapper->value(), 0x0bbac0de);
+                EXPECT_EQ((*globalPersistent)->value(), 0x0ed0cabb);
             }
             yield();
         }