Port regexp tests from V8 to Dart.

tests/corelib/regexp/loop-capture_test.dart

 // Copyright (c) 2014, 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.
 
+import 'util.dart';
 import 'package:expect/expect.dart';
 
-foo() {
-  try {
-    try {
-      return 1;
-    } catch (e1) {
-    } finally {
-      return 3;
-    }
-  } catch (e2) {
-  } finally  {
-    return 5;
-  }
+void main() {
+  shouldBe(new RegExp(r"(?:(a)|(b)|(c))+").firstMatch("abc"), ["abc",null,null,"c"]);
+  shouldBe(new RegExp(r"(?:(a)|b)*").firstMatch("ab"), ["ab",null]);
 }
-
-
-main() {
-  Expect.equals(5, foo());
-}