Add some support for the code-point code-unit distinction.

tests/corelib/reg_exp_unicode_test.dart

+// Copyright (c) 2011, 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.
+// Dart test for testing regular expressions in Dart.
+
+main() {
+  String str = "\u{10000}";
+
+  // Dot will match surrogates too (ideally it should match a pair).
+  Expect.isTrue(new RegExp(r'^..?$').hasMatch(str));
+
+  // Surrogate pair in a RegExp.
+  Expect.isTrue(new RegExp('^\u{10000}\$').hasMatch(str));
+
+  // Mormon characters should work too.
+  String mitt = "My name is 𐐣𐐮𐐻";
+  Expect.isTrue(new RegExp(r'𐐣𐐮𐐻$').hasMatch(mitt));
+
+  // Character classes sort of work, but the surrogates are treated as separate
+  // characters.
+  Expect.isTrue(new RegExp(r'[𐐣𐐮𐐻]+$').hasMatch(mitt));
+}