Introduce IsUndefined(Isolate*) and IsTheHole(Isolate*)

src/json-stringifier.cc

Index: src/json-stringifier.cc
diff --git a/src/json-stringifier.cc b/src/json-stringifier.cc
index 6293b0c4593944f30a1832dbf34f7fc6931b6cb2..9d19110d10d945e35783a3d9e9142d60601e3116 100644
--- a/src/json-stringifier.cc
+++ b/src/json-stringifier.cc
@@ -91,7 +91,9 @@ MaybeHandle<Object> JsonStringifier::Stringify(Handle<Object> object,
                                                Handle<Object> replacer,
                                                Handle<Object> gap) {
   if (!InitializeReplacer(replacer)) return MaybeHandle<Object>();
-  if (!gap->IsUndefined() && !InitializeGap(gap)) return MaybeHandle<Object>();
+  if (!gap->IsUndefined(isolate_) && !InitializeGap(gap)) {
+    return MaybeHandle<Object>();
+  }
   Result result = SerializeObject(object);
   if (result == UNCHANGED) return factory()->undefined_value();
   if (result == SUCCESS) return builder_.Finish();