Refactor the Heap into ThreadHeap to prepare for per thread heaps

third_party/WebKit/Source/platform/heap/PersistentNode.h

Index: third_party/WebKit/Source/platform/heap/PersistentNode.h
diff --git a/third_party/WebKit/Source/platform/heap/PersistentNode.h b/third_party/WebKit/Source/platform/heap/PersistentNode.h
index 338adf2b4ca7ba114ac580986d81928571d3d502..f21aa4306ccc4f1d730209f7298c90f7fd752944 100644
--- a/third_party/WebKit/Source/platform/heap/PersistentNode.h
+++ b/third_party/WebKit/Source/platform/heap/PersistentNode.h
@@ -188,6 +188,38 @@ private:
     Mutex m_mutex;
 };
 
+class XThreadPersistentRegion final {
+public:
+    XThreadPersistentRegion() : m_persistentRegion(adoptPtr(new PersistentRegion)) { }
+
+    PersistentNode* allocatePersistentNode(void* self, TraceCallback trace)
+    {
+        MutexLocker lock(m_mutex);
+        return m_persistentRegion->allocatePersistentNode(self, trace);
+    }
+
+    void freePersistentNode(PersistentNode* persistentNode)
+    {
+        MutexLocker lock(m_mutex);
+        m_persistentRegion->freePersistentNode(persistentNode);
+    }
+
+    void tracePersistentNodes(Visitor* visitor)
+    {
+        MutexLocker lock(m_mutex);
+        m_persistentRegion->tracePersistentNodes(visitor);
+    }
+
+    void prepareForThreadStateTermination(ThreadState*);
+
+private:
+    // We don't make CrossThreadPersistentRegion inherit from PersistentRegion
+    // because we don't want to virtualize performance-sensitive methods
+    // such as PersistentRegion::allocate/freePersistentNode.
+    OwnPtr<PersistentRegion> m_persistentRegion;
+    Mutex m_mutex;
+};
+
 } // namespace blink
 
 #endif