Port and integrate the irregexp engine from V8

tests/language/regex/UC16_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';
+
+void main() {
+  // UC16
+  // Characters used:
+  // "\u03a3\u03c2\u03c3\u039b\u03bb" - Sigma, final sigma, sigma, Lambda, lamda
+  shouldBe(new RegExp(r"x(.)\1x", caseSensitive: false).firstMatch("x\u03a3\u03c3x"),
+      ["x\u03a3\u03c3x", "\u03a3"], "backref-UC16");
+  assertFalse(new RegExp(r"x(...)\1", caseSensitive: false).hasMatch("x\u03a3\u03c2\u03c3\u03c2\u03c3"),
+              "\1 ASCII, string short");
+  assertTrue(new RegExp(r"\u03a3((?:))\1\1x", caseSensitive: false).hasMatch("\u03c2x"), "backref-UC16-empty");
+  assertTrue(new RegExp(r"x(?:...|(...))\1x", caseSensitive: false).hasMatch("x\u03a3\u03c2\u03c3x"),
+            "backref-UC16-uncaptured");
+  assertTrue(new RegExp(r"x(?:...|(...))\1x", caseSensitive: false).hasMatch("x\u03c2\u03c3\u039b\u03a3\u03c2\u03bbx"),
+            "backref-UC16-backtrack");
+  var longUC16String = "x\u03a3\u03c2\u039b\u03c2\u03c3\u03bb\u03c3\u03a3\u03bb";
+  shouldBe(new RegExp(r"x(...)\1\1", caseSensitive: false).firstMatch(longUC16String),
+          [longUC16String, longUC16String.substring(1,4)],
+          "backref-UC16-twice");
+
+  assertFalse(new RegExp(r"\xc1", caseSensitive: false).hasMatch('fooA'), "quickcheck-uc16-pattern-ascii-subject");
+  assertFalse(new RegExp(r"[\xe9]").hasMatch('i'), "charclass-uc16-pattern-ascii-subject");
+  assertFalse(new RegExp(r"\u5e74|\u6708").hasMatch('t'), "alternation-uc16-pattern-ascii-subject");
+}