Port regexp tests from V8 to Dart.

tests/corelib/regexp/look-ahead_test.dart

Index: tests/corelib/regexp/look-ahead_test.dart
diff --git a/tests/corelib/regexp/look-ahead_test.dart b/tests/corelib/regexp/look-ahead_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b1dd53cfa06705feec4e391ceab628b4886f48b8
--- /dev/null
+++ b/tests/corelib/regexp/look-ahead_test.dart
@@ -0,0 +1,15 @@
+// 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';
+
+void main() {
+  description(
+  'Test for regression against <a href="https://bugs.webkit.org/show_bug.cgi?id=41458">Yarr Interpreter is crashing in some cases of look-ahead regex patterns</a>'
+  );
+
+  shouldBe(firstMatch("ab", new RegExp(r"a(?=b|c)")), ["a"]);
+  shouldBe(firstMatch("abd", new RegExp(r"a(?=c|b)|d")), ["a"]);
+}