Check function type equivalence

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 157 matching lines @@
       default:
         throw new UnsupportedError('Unsupported equivalence: '
             '$a (${a.runtimeType}) vs $b (${b.runtimeType})');
     }
   }
 
   bool typeEquivalence(ResolutionDartType a, DartType b,
       {TestStrategy strategy}) {
     if (identical(a, b)) return true;
     if (a == null || b == null) return false;
+    a = unalias(a);
     strategy ??= defaultStrategy;
     switch (a.kind) {
       case ResolutionTypeKind.DYNAMIC:
         return b is DynamicType;
       case ResolutionTypeKind.VOID:
         return b is VoidType;
       case ResolutionTypeKind.INTERFACE:
         if (b is InterfaceType) {
           ResolutionInterfaceType aType = a;
           return strategy.testElements(a, b, 'element', a.element, b.element) &&
@@ skipping 118 matching lines @@
     for (ConstructorElement constructor in element.constructors) {
       if (!constructor.isRedirectingFactory) {
         return true;
       }
     }
     // The class cannot itself be instantiated.
     return false;
   }
   return true;
 }