Refactor the Heap into ThreadHeap to prepare for per thread heaps

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

Index: third_party/WebKit/Source/platform/heap/Visitor.h
diff --git a/third_party/WebKit/Source/platform/heap/Visitor.h b/third_party/WebKit/Source/platform/heap/Visitor.h
index c65907728e1f115ccd2c8b95dc6f359b79f05c7e..1035ee950f51e49562fc964970843b2905e1215d 100644
--- a/third_party/WebKit/Source/platform/heap/Visitor.h
+++ b/third_party/WebKit/Source/platform/heap/Visitor.h
@@ -121,6 +121,8 @@ public:
 template<typename Derived>
 class VisitorHelper {
 public:
+    VisitorHelper() : m_threadState(ThreadState::current()) {}
+
     // One-argument templated mark method. This uses the static type of
     // the argument to get the TraceTrait. By default, the mark method
     // of the TraceTrait just calls the virtual two-argument mark method on this
@@ -281,9 +283,13 @@ public:
         Derived::fromHelper(this)->registerWeakMembers(object, object, callback);
     }
 
+    inline ThreadState* threadState() const { return m_threadState; }
+
 private:
     template<typename T>
     static void handleWeakCell(Visitor* self, void* object);
+
+    ThreadState* m_threadState;
 };
 
 // Visitor is used to traverse the Blink object graph. Used for the