Add %GetUndetectable() test intrinsic and add tests for undetectables.

src/runtime/runtime-test.cc

Index: src/runtime/runtime-test.cc
diff --git a/src/runtime/runtime-test.cc b/src/runtime/runtime-test.cc
index ddf2e9d6b46a6c7b6b848ae9754f293ef27381f2..6b238cea782b9ac2c12e914faadce0234c339f78 100644
--- a/src/runtime/runtime-test.cc
+++ b/src/runtime/runtime-test.cc
@@ -212,6 +212,18 @@ RUNTIME_FUNCTION(Runtime_GetOptimizationCount) {
 }
 
 
+RUNTIME_FUNCTION(Runtime_GetUndetectable) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 0);
+
+  Local<v8::ObjectTemplate> desc =
+      v8::ObjectTemplate::New((v8::Isolate*)isolate);
+  desc->MarkAsUndetectable();  // undetectable
+  Local<v8::Object> obj = desc->NewInstance();
+  return *Utils::OpenHandle(*obj);
+}
+
+
 RUNTIME_FUNCTION(Runtime_ClearFunctionTypeFeedback) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);