Add Uint32 representation

tests/language/vm/uint32_shift_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.
+// VMOptions=--optimization_counter_threshold=10
+
+import 'package:expect/expect.dart';
+
+class Good {
+  use(x) { return x & 0x1; }
+}
+
+class Bad {
+  use(x) { return x & 0x100000000; }
+}
+
+f(o, x) => o.use(x << 1);
+
+main() {
+  final good = new Good();
+  final bad = new Bad();
+  for (var i = 0; i < 20000; i++) {
+    Expect.equals(0, f(good, 0x80000000));
+  }
+  Expect.equals(0x100000000, f(bad, 0x80000000));
+}
+