Add stub versions of KernelInferrerEngine and friends

tests/compiler/dart2js/list_tracer2_test.dart

Index: tests/compiler/dart2js/list_tracer2_test.dart
diff --git a/tests/compiler/dart2js/list_tracer2_test.dart b/tests/compiler/dart2js/list_tracer2_test.dart
index 9f7f51e7ae7d48e48a362c4aaf7a471c87115372..3e1d17b5d7a20394d1f4e1e91a1ba0cc78a7c72c 100644
--- a/tests/compiler/dart2js/list_tracer2_test.dart
+++ b/tests/compiler/dart2js/list_tracer2_test.dart
@@ -28,7 +28,7 @@ void main() {
         var closedWorld = typesInferrer.closedWorld;
 
         checkType(String name, type) {
-          var element = findElement(compiler, name);
+          MemberElement element = findElement(compiler, name);
           ContainerTypeMask mask = typesInferrer.getTypeOfMember(element);
           Expect.equals(type, simplify(mask.elementType, closedWorld), name);
         }