Do not shortcut union of keys if lhs is empty.

test/cctest/test-api.cc

 // Copyright 2007-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 11709 matching lines @@
   context->Global()->Set(v8_str("re"), re);
   ExpectTrue("re.test('FoobarbaZ')");
 
   v8::TryCatch try_catch;
   re = v8::RegExp::New(v8_str("foo["), v8::RegExp::kNone);
   CHECK(re.IsEmpty());
   CHECK(try_catch.HasCaught());
   context->Global()->Set(v8_str("ex"), try_catch.Exception());
   ExpectTrue("ex instanceof SyntaxError");
 }
+
+
+static v8::Handle<v8::Value> Getter(v8::Local<v8::String> property,
+                                    const v8::AccessorInfo& info ) {
+  return v8_str("42!");
+}
+
+
+static v8::Handle<v8::Array> Enumerator(const v8::AccessorInfo& info) {
+  v8::Handle<v8::Array> result = v8::Array::New();
+  result->Set(0, v8_str("universalAnswer"));
+  return result;
+}
+
+
+TEST(NamedEnumeratorAndForIn) {
+  v8::HandleScope handle_scope;
+  LocalContext context;
+  v8::Context::Scope context_scope(context.local());
+
+  v8::Handle<v8::ObjectTemplate> tmpl = v8::ObjectTemplate::New();
+  tmpl->SetNamedPropertyHandler(Getter, NULL, NULL, NULL, Enumerator);
+  context->Global()->Set(v8_str("o"), tmpl->NewInstance());
+  v8::Handle<v8::Array> result = v8::Handle<v8::Array>::Cast(CompileRun(
+        "var result = []; for (var k in o) result.push(k); result"));
+  CHECK_EQ(1, result->Length());
+  CHECK_EQ(v8_str("universalAnswer"), result->Get(0));
+}