Port the remaining of dart:coreimpl to the unified corelib.

corelib/unified/coreimpl/options.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-#library('test2.dart');
+class RuntimeOptions implements Options {
+  external List<String> get arguments();
 
-#source('../$SRC/test2a.dart');
+  external String get executable();
 
-int test2() {
-  var result = test2a();
-  Expect.equals(2, result);
-  return result;
+  external String get script();
 }