Add stub versions of KernelInferrerEngine and friends

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';
 import 'type_mask_test_helper.dart';
 
 const String TEST = """
@@ skipping 104 matching lines @@
 """;
 
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   asyncTest(() => compiler.run(uri).then((_) {
         var typesInferrer = compiler.globalInference.typesInferrerInternal;
         var closedWorld = typesInferrer.closedWorld;
 
         checkReturn(String name, type) {
-          var element = findElement(compiler, name);
+          MemberElement element = findElement(compiler, name);
           Expect.equals(
               type,
               simplify(
                   typesInferrer.getReturnTypeOfMember(element), closedWorld),
               name);
         }
 
         checkReturn('returnInt1', closedWorld.commonMasks.uint31Type);
         checkReturn('returnInt2', closedWorld.commonMasks.uint31Type);
         checkReturn('returnInt3', closedWorld.commonMasks.uint31Type);
@@ skipping 16 matching lines @@
               type,
               simplify(
                   typesInferrer.getReturnTypeOfMember(element), closedWorld));
         }
 
         dynamic cls = findElement(compiler, 'A');
         checkReturnInClass(
             'A', 'foo', new TypeMask.nonNullExact(cls, closedWorld));
       }));
 }