Add stub versions of KernelInferrerEngine and friends

tests/compiler/dart2js/list_tracer_typed_data_length_test.dart

Index: tests/compiler/dart2js/list_tracer_typed_data_length_test.dart
diff --git a/tests/compiler/dart2js/list_tracer_typed_data_length_test.dart b/tests/compiler/dart2js/list_tracer_typed_data_length_test.dart
index 422ad7f0051c9435d0aa75ef7580df055ccc1401..3e082fdcff8e29cafe20346146db3f04ae77838d 100644
--- a/tests/compiler/dart2js/list_tracer_typed_data_length_test.dart
+++ b/tests/compiler/dart2js/list_tracer_typed_data_length_test.dart
@@ -4,6 +4,7 @@
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
+import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/types/types.dart' show ContainerTypeMask, TypeMask;
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/world.dart' show ClosedWorld;
@@ -34,7 +35,7 @@ void main() {
     ClosedWorld closedWorld = typesInferrer.closedWorld;
 
     checkType(String name, type, length) {
-      var element = findElement(compiler, name);
+      MemberElement element = findElement(compiler, name);
       TypeMask mask = typesInferrer.getTypeOfMember(element);
       Expect.isTrue(mask.isContainer);
       ContainerTypeMask container = mask;