Share Maps for ElementsKind transitions

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 5c8a3142aedb88769d9db6978f5571da8a572faf..52d75aad3b003f8afb878bb2c1c2ec12f45bbc1d 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -3310,22 +3310,12 @@ void PrepareExternalArrayElements(i::Handle<i::JSObject> object,
   i::Handle<i::ExternalArray> array =
       isolate->factory()->NewExternalArray(length, array_type, data);
 
-  // If the object already has external elements, create a new, unique
-  // map if the element type is now changing, because assumptions about
-  // generated code based on the receiver's map will be invalid.
-  i::Handle<i::HeapObject> elements(object->elements());
-  bool cant_reuse_map =
-      elements->map()->IsUndefined() ||
-      !elements->map()->has_external_array_elements() ||
-      elements->map() != isolate->heap()->MapForExternalArrayType(array_type);
-  if (cant_reuse_map) {
-    i::Handle<i::Map> external_array_map =
-        isolate->factory()->GetElementsTransitionMap(
-            i::Handle<i::Map>(object->map()),
-            GetElementsKindFromExternalArrayType(array_type),
-            object->HasFastProperties());
-    object->set_map(*external_array_map);
-  }
+  i::Handle<i::Map> external_array_map =
+      isolate->factory()->GetElementsTransitionMap(
+          object,
+          GetElementsKindFromExternalArrayType(array_type));
+
+  object->set_map(*external_array_map);
   object->set_elements(*array);
 }