Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/kernel/test_helpers.dart

 // Copyright (c) 2016, 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.
 
 library dart2js.kernel.equivalence;
 
 import 'package:compiler/src/common/backend_api.dart';
 import 'package:compiler/src/common/resolution.dart';
 import 'package:compiler/src/common/work.dart';
 import 'package:compiler/src/constants/expressions.dart';
@@ skipping 236 matching lines @@
 }
 
 /// Visitor the performers unaliasing of all typedefs nested within a
 /// [ResolutionDartType].
 class Unaliaser
     extends BaseResolutionDartTypeVisitor<dynamic, ResolutionDartType> {
   const Unaliaser();
 
   @override
   ResolutionDartType visit(ResolutionDartType type, [_]) =>
+      // ignore: ARGUMENT_TYPE_NOT_ASSIGNABLE
       type.accept(this, null);
 
   @override
   ResolutionDartType visitType(ResolutionDartType type, _) => type;
 
   List<ResolutionDartType> visitList(List<ResolutionDartType> types) =>
       types.map(visit).toList();
 
   @override
   ResolutionDartType visitInterfaceType(ResolutionInterfaceType type, _) {
@@ skipping 30 matching lines @@
     for (ConstructorElement constructor in element.constructors) {
       if (!constructor.isRedirectingFactory) {
         return true;
       }
     }
     // The class cannot itself be instantiated.
     return false;
   }
   return true;
 }