Fix Unicode issues in dart2js and dart2dart.

tests/corelib/string_from_list_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.
 
 class StringFromListTest {
   static testMain() {
     Expect.equals("", new String.fromCharCodes(new List(0)));
     Expect.equals("", new String.fromCharCodes([]));
     Expect.equals("", new String.fromCharCodes(const []));
     Expect.equals("AB", new String.fromCharCodes([65, 66]));
     Expect.equals("AB", new String.fromCharCodes(const [65, 66]));
+    Expect.equals("Ærø", new String.fromCharCodes(const [0xc6, 0x72, 0xf8]));
+    Expect.equals("\u{1234}", new String.fromCharCodes([0x1234]));
+    Expect.equals("\u{12345}*", new String.fromCharCodes([0x12345, 42]));
     Expect.equals("", new String.fromCharCodes(new List()));
-    var a = new List();
-    a.add(65);
-    a.add(66);
-    Expect.equals("AB", new String.fromCharCodes(a));
+    {
+      var a = new List();
+      a.add(65);
+      a.add(66);
+      Expect.equals("AB", new String.fromCharCodes(a));
+    }
   }
 }
 
 main() {
   StringFromListTest.testMain();
 }