Eagerly parse expected transitions in JSON.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 1dc170410951f7e01238815dae3b62340e6f6721..1890eb40954d479ec01dd4339a498f13a0f8de02 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2602,13 +2602,18 @@ MaybeObject* JSObject::GetElementsTransitionMapSlow(ElementsKind to_kind) {
     return start_map->CopyAsElementsKind(to_kind, OMIT_TRANSITION);
   }
 
-  Map* closest_map = FindClosestElementsTransition(start_map, to_kind);
+  return start_map->AsElementsKind(to_kind);
+}
+
 
-  if (closest_map->elements_kind() == to_kind) {
+MaybeObject* Map::AsElementsKind(ElementsKind kind) {
+  Map* closest_map = FindClosestElementsTransition(this, kind);
+
+  if (closest_map->elements_kind() == kind) {
     return closest_map;
   }
 
-  return AddMissingElementsTransitions(closest_map, to_kind);
+  return AddMissingElementsTransitions(closest_map, kind);
 }
 
 
@@ -3073,6 +3078,13 @@ void JSObject::AddFastPropertyUsingMap(Handle<JSObject> object,
 }
 
 
+void JSObject::TransitionToMap(Handle<JSObject> object, Handle<Map> map) {
+  CALL_HEAP_FUNCTION_VOID(
+      object->GetIsolate(),
+      object->TransitionToMap(*map));
+}
+
+
 MaybeObject* JSObject::SetPropertyForResult(LookupResult* lookup,
                                             Name* name_raw,
                                             Object* value_raw,