Add Object::IsNullOrUndefined(Isolate*) helper method

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 244e66d4d116514df95ea8d47bc4e25345218c98..5a37c5003d5a330f90d2695c176644a2cbe863c7 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -218,6 +218,16 @@ HEAP_OBJECT_TYPE_LIST(IS_TYPE_FUNCTION_DEF)
 ODDBALL_LIST(IS_TYPE_FUNCTION_DEF)
 #undef IS_TYPE_FUNCTION_DEF
 
+bool Object::IsNullOrUndefined(Isolate* isolate) const {
+  Heap* heap = isolate->heap();
+  return this == heap->null_value() || this == heap->undefined_value();
+}
+
+bool HeapObject::IsNullOrUndefined(Isolate* isolate) const {
+  Heap* heap = isolate->heap();
+  return this == heap->null_value() || this == heap->undefined_value();
+}
+
 bool HeapObject::IsString() const {
   return map()->instance_type() < FIRST_NONSTRING_TYPE;
 }