Add UInt32 and UInt31 types to better infer bit operations.

tests/compiler/dart2js/value_range_test.dart

 // Copyright (c) 2012, 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";
 import 'compiler_helper.dart';
 
 const int REMOVED = 0;
 const int ABOVE_ZERO = 1;
 const int BELOW_LENGTH = 2;
@@ skipping 316 matching lines @@
   class JSDouble extends JSNumber {
   }
   class JSNull {
   }
   class JSBool {
   }
   class JSFunction {
   }
   class ObjectInterceptor {
   }
+  class JSUInt32 extends JSInt {}
+  class JSUInt31 extends JSUInt32 {}
   getInterceptor(x) {}''';
 
 expect(String code, int kind) {
   String generated = compile(
       code,
       coreSource: DEFAULT_CORELIB_WITH_LIST_INTERFACE,
       interceptorsSource: INTERCEPTORSLIB_WITH_MEMBERS);
   switch (kind) {
     case REMOVED:
       Expect.isTrue(!generated.contains('ioore'));
@@ skipping 32 matching lines @@
       break;
   }
 }
 
 
 main() {
   for (int i = 0; i < TESTS.length;  i += 2) {
     expect(TESTS[i], TESTS[i + 1]);
   }
 }