[heap] Prevent leakage of GCCallbacksScope outside of heap.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index aa08d449970b4f7f89cadcf037feff8dd72a848d..09593c24adc78a7de2d35ab2a7c9cf03c4201da3 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -2430,18 +2430,6 @@ class AlwaysAllocateScope {
 };
 
 
-class GCCallbacksScope {
- public:
-  explicit inline GCCallbacksScope(Heap* heap);
-  inline ~GCCallbacksScope();
-
-  inline bool CheckReenter();
-
- private:
-  Heap* heap_;
-};
-
-
 // Visitor class to verify interior pointers in spaces that do not contain
 // or care about intergenerational references. All heap object pointers have to
 // point into the heap to a location that has a map pointer at its first word.