Use index in J/KTypeVariable and fix remaining inequivalence

tests/compiler/dart2js/js_model/model_test.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 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/kernel/kernel_backend_strategy.dart';
 import '../kernel/compile_from_dill_test_helper.dart';
 import '../serialization/helper.dart';
 
@@ skipping 22 matching lines @@
       print(
           '--- running test code -------------------------------------------');
       print(test.sources.values.first);
       print('----------------------------------------------------------------');
     }
     await runTest(test.entryPoint, test.sources,
         verbose: arguments.verbose,
         skipWarnings: skipWarnings,
         skipErrors: skipErrors,
         options: options,
-        expectAstEquivalence: false,
+        expectAstEquivalence: true,
         expectIdenticalOutput: false);
   }
 }