Add stub versions of KernelInferrerEngine and friends

tests/compiler/dart2js/simple_inferrer_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 'package:compiler/src/types/types.dart' show TypeMask;
 import 'type_mask_test_helper.dart';
 
 import 'compiler_helper.dart';
@@ skipping 714 matching lines @@
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   compiler.diagnosticHandler = createHandler(compiler, TEST);
   asyncTest(() => compiler.run(uri).then((_) {
         var typesInferrer = compiler.globalInference.typesInferrerInternal;
         var closedWorld = typesInferrer.closedWorld;
         var commonMasks = closedWorld.commonMasks;
 
         checkReturn(String name, type) {
-          var element = findElement(compiler, name);
+          MemberElement element = findElement(compiler, name);
           Expect.equals(
               type,
               simplify(
                   typesInferrer.getReturnTypeOfMember(element), closedWorld),
               name);
         }
 
         var interceptorType = commonMasks.interceptorType;
 
         checkReturn('returnNum1', commonMasks.numType);
@@ skipping 135 matching lines @@
         checkReturn('testSpecialization3', commonMasks.uint31Type.nullable());
         checkReturn('testReturnNull1', commonMasks.nullType);
         checkReturn('testReturnNull2', commonMasks.nullType);
         checkReturn('testReturnNull3', commonMasks.dynamicType);
         checkReturn('testReturnNull4', commonMasks.nullType);
         checkReturn('testReturnNull5', commonMasks.nullType);
         checkReturn('testReturnNull6', commonMasks.dynamicType);
         checkReturn('testReturnNotEquals', commonMasks.boolType);
       }));
 }