Introduce {FAST,SLOW}_STRING_WRAPPER_ELEMENTS

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 634d1b3c7d11b55d204c2a1c4649ae61ec1c1b27..8d05e39524b5ef00d7296409bdb61124f6a4cc8c 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -3515,7 +3515,8 @@ AllocationResult Heap::AllocateJSObjectFromMap(
 
   // Initialize the JSObject.
   InitializeJSObjectFromMap(js_obj, properties, map);
-  DCHECK(js_obj->HasFastElements() || js_obj->HasFixedTypedArrayElements());
+  DCHECK(js_obj->HasFastElements() || js_obj->HasFixedTypedArrayElements() ||
+         js_obj->HasFastStringWrapperElements());
   return js_obj;
 }