Add Uint32 representation

tests/language/vm/uint32_right_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';
+
+trunc(x) => x & 0xFFFFFFFF;
+
+foo(t, x) => t(x >> 15);
+
+main() {
+  for (var i = 0; i < 20000; i++) {
+    Expect.equals(0x00010000, foo(trunc, 0x80000000));
+  }
+  for (var i = 0; i < 20000; i++) {
+    Expect.equals(0x10000000, foo(trunc, 0x80000000000));
+  }
+}
+