Add stub versions of KernelInferrerEngine and friends

tests/compiler/dart2js/inference/inference_test_helper.dart

 // Copyright (c) 2017, 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:compiler/src/common.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/entities.dart';
 import 'package:compiler/src/tree/nodes.dart';
 import 'package:compiler/src/types/types.dart';
@@ skipping 24 matching lines @@
 
   TypeMaskComputer(DiagnosticReporter reporter, Map<Id, String> actualMap,
       Map<Id, Spannable> spannableMap, ResolvedAst resolvedAst, this.results)
       : result = results.resultOfMember(resolvedAst.element as MemberElement),
         super(reporter, actualMap, spannableMap, resolvedAst);
 
   @override
   String computeElementValue(AstElement element) {
     GlobalTypeInferenceElementResult elementResult;
     if (element.isParameter) {
-      elementResult = results.resultOfParameter(element);
+      ParameterElement parameter = element;
+      elementResult = results.resultOfParameter(parameter);
     } else if (element.isLocal) {
       LocalFunctionElement localFunction = element;
       elementResult = results.resultOfMember(localFunction.callMethod);
     } else {
-      elementResult = results.resultOfMember(element);
+      MemberElement member = element;
+      elementResult = results.resultOfMember(member);
     }
 
     TypeMask value =
         element.isFunction ? elementResult.returnType : elementResult.type;
     return value != null ? '$value' : null;
   }
 
   @override
   String computeNodeValue(Node node, [AstElement element]) {
     if (node is Send) {
       TypeMask value = result.typeOfSend(node);
       return value != null ? '$value' : null;
     } else if (element != null && element.isLocal) {
       return computeElementValue(element);
     }
     return null;
   }
 }