[runtime] More LookupIterator / Transition related performance tweaks

src/field-type.h

Index: src/field-type.h
diff --git a/src/field-type.h b/src/field-type.h
index e390fca53ee39cbd3af0a1aa63a6915725c72ab0..eb7ffcab477ae6b505288c4aaf6c540d8d2cd54c 100644
--- a/src/field-type.h
+++ b/src/field-type.h
@@ -22,8 +22,15 @@ class FieldType : public Object {
   static Handle<FieldType> Class(i::Handle<i::Map> map, Isolate* isolate);
   static FieldType* cast(Object* object);
 
-  bool NowContains(Object* value);
-  bool NowContains(Handle<Object> value);
+  bool NowContains(Object* value) {
+    if (this == Any()) return true;
+    if (this == None()) return false;
+    if (!value->IsHeapObject()) return false;
+    return HeapObject::cast(value)->map() == Map::cast(this);
+  }
+
+  bool NowContains(Handle<Object> value) { return NowContains(*value); }
+
   bool IsClass();
   Handle<i::Map> AsClass();
   bool IsNone() { return this == None(); }