Add UInt32 and UInt31 types to better infer bit operations.

tests/compiler/dart2js/simple_inferrer_closure_test.dart

 // Copyright (c) 2013, 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 "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 
 const String TEST = """
 returnInt1() {
@@ skipping 105 matching lines @@
 
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   asyncTest(() => compiler.runCompiler(uri).then((_) {
     var typesInferrer = compiler.typesTask.typesInferrer;
 
     checkReturn(String name, type) {
       var element = findElement(compiler, name);
       Expect.equals(type,
-          typesInferrer.getReturnTypeOfElement(element).simplify(compiler));
+          typesInferrer.getReturnTypeOfElement(element).simplify(compiler),
+          name);
     }
 
-    checkReturn('returnInt1', compiler.typesTask.intType);
-    checkReturn('returnInt2', compiler.typesTask.intType);
-    checkReturn('returnInt3', compiler.typesTask.intType);
-    checkReturn('returnInt4', compiler.typesTask.intType);
-    checkReturn('returnIntOrNull', compiler.typesTask.intType.nullable());
+    checkReturn('returnInt1', compiler.typesTask.uint31Type);
+    checkReturn('returnInt2', compiler.typesTask.uint31Type);
+    checkReturn('returnInt3', compiler.typesTask.uint31Type);
+    checkReturn('returnInt4', compiler.typesTask.uint31Type);
+    checkReturn('returnIntOrNull', compiler.typesTask.uint31Type.nullable());
 
     checkReturn('returnDyn1', compiler.typesTask.dynamicType.nonNullable());
     checkReturn('returnDyn2', compiler.typesTask.dynamicType.nonNullable());
     checkReturn('returnDyn3', compiler.typesTask.dynamicType.nonNullable());
     checkReturn('returnNum1', compiler.typesTask.numType);
 
     checkReturnInClass(String className, String methodName, type) {
       var cls = findElement(compiler, className);
       var element = cls.lookupLocalMember(methodName);
       Expect.equals(type,
           typesInferrer.getReturnTypeOfElement(element).simplify(compiler));
     }
     var cls = findElement(compiler, 'A');
     checkReturnInClass('A', 'foo', new TypeMask.nonNullExact(cls));
   }));
 }