Simplify PrepareForDataProperty in the IsElement case

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index fa4d66903ca8d6fbeabfc699d6a8a7ebbcabcf0f..37c03057eede89ca42b1ec2b8059b228ca5b6b68 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -5766,8 +5766,6 @@ class Map: public HeapObject {
   static Handle<Map> PrepareForDataProperty(Handle<Map> old_map,
                                             int descriptor_number,
                                             Handle<Object> value);
-  static Handle<Map> PrepareForDataElement(Handle<Map> old_map,
-                                           Handle<Object> value);
 
   static Handle<Map> Normalize(Handle<Map> map, PropertyNormalizationMode mode,
                                const char* reason);
@@ -6030,6 +6028,7 @@ class Map: public HeapObject {
   bool IsJSObjectMap() {
     return instance_type() >= FIRST_JS_OBJECT_TYPE;
   }
+  bool IsJSArrayMap() { return instance_type() == JS_ARRAY_TYPE; }
   bool IsStringMap() { return instance_type() < FIRST_NONSTRING_TYPE; }
   bool IsJSProxyMap() {
     InstanceType type = instance_type();