Port and integrate the irregexp engine from V8

tests/language/regex/alternatives_test.dart

Index: tests/language/regex/alternatives_test.dart
diff --git a/tests/language/regex/alternatives_test.dart b/tests/language/regex/alternatives_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..866d98a204dc99ef5a6780dfa5f665117d09b1aa
--- /dev/null
+++ b/tests/language/regex/alternatives_test.dart
@@ -0,0 +1,28 @@
+// 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 regular expression processing with alternatives.'
+  );
+
+  var s1 = "<p>content</p>";
+  shouldBe(firstMatch(s1, new RegExp(r"<((\\/([^>]+)>)|(([^>]+)>))")), ["<p>","p>",null,null,"p>","p"]);
+  shouldBe(firstMatch(s1, new RegExp(r"<((ABC>)|(\\/([^>]+)>)|(([^>]+)>))")), ["<p>","p>",null,null,null,"p>","p"]);
+  shouldBe(firstMatch(s1, new RegExp(r"<(a|\\/p|.+?)>")), ["<p>","p"]);
+
+  // Force YARR to use Interpreter by using iterative parentheses
+  shouldBe(firstMatch(s1, new RegExp(r"<((\\/([^>]+)>)|((([^>])+)>))")), ["<p>","p>",null,null,"p>","p","p"]);
+  shouldBe(firstMatch(s1, new RegExp(r"<((ABC>)|(\\/([^>]+)>)|((([^>])+)>))")), ["<p>","p>",null,null,null,"p>","p","p"]);
+  shouldBe(firstMatch(s1, new RegExp(r"<(a|\\/p|(.)+?)>")), ["<p>","p","p"]);
+
+  // Force YARR to use Interpreter by using backreference
+  var s2 = "<p>p</p>";
+  shouldBe(firstMatch(s2, new RegExp(r"<((\\/([^>]+)>)|(([^>]+)>))\5")), ["<p>p","p>",null,null,"p>","p"]);
+  shouldBe(firstMatch(s2, new RegExp(r"<((ABC>)|(\\/([^>]+)>)|(([^>]+)>))\6")), ["<p>p","p>",null,null,null,"p>","p"]);
+  shouldBe(firstMatch(s2, new RegExp(r"<(a|\\/p|.+?)>\1")), ["<p>p","p"]);
+}