Fixes scanning of Utf16 surrogate pairs in string literals.

tests/language/unicode_hash_test.dart

Index: tests/language/unicode_hash_test.dart
===================================================================
--- tests/language/unicode_hash_test.dart	(revision 0)
+++ tests/language/unicode_hash_test.dart	(revision 0)
@@ -0,0 +1,10 @@
+// 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.
+
+import "package:expect/expect.dart";
+
+main() {
+  Expect.equals("\u{10412}", "𐐒");  // Second string is literal U+10412.
+  Expect.equals("\u{10412}".hashCode, "𐐒".hashCode);
+}