Add most equivalence tests to js_model/model_test

pkg/compiler/lib/src/js_model/elements.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.
 
 library dart2js.js_model.elements;
 
 import '../common_elements.dart';
 import '../constants/constant_system.dart';
 import '../elements/elements.dart';
 import '../elements/entities.dart';
@@ skipping 488 matching lines @@
   JField(int memberIndex, JLibrary library, JClass enclosingClass, Name name,
       {bool isStatic, this.isAssignable, this.isConst})
       : super(memberIndex, library, enclosingClass, name, isStatic: isStatic);
 
   @override
   bool get isField => true;
 
   String get _kind => 'field';
 }
 
-class JTypeVariable implements TypeVariableEntity {
+class JTypeVariable implements TypeVariableEntity, IndexedTypeVariable {
   final Entity typeDeclaration;
   final String name;
   final int index;
 
   JTypeVariable(this.typeDeclaration, this.name, this.index);
 
   String toString() =>
       '${jsElementPrefix}type_variable(${typeDeclaration.name}.$name)';
 }
 
@@ skipping 200 matching lines @@
 
   @override
   bool get isFunctionApplyUsed => _backendUsage.isFunctionApplyUsed;
 
   @override
   bool get isMirrorsUsed => _backendUsage.isMirrorsUsed;
 
   @override
   bool get isNoSuchMethodUsed => _backendUsage.isNoSuchMethodUsed;
 }