Fix serialization of forwarding constructors.

tests/compiler/dart2js/serialization_test_helper.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.serialization_test_helper;
 
 import 'dart:io';
 import 'memory_compiler.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common/resolution.dart';
@@ skipping 322 matching lines @@
     Compiler compiler1,
     Compiler compiler2,
     {bool verbose: false}) {
   checkLoadedLibraryMembers(
       compiler1,
       compiler2,
       (Element member1) {
         return compiler1.resolution.hasResolutionImpact(member1);
       },
       checkImpacts,
-      verbose: true);
+      verbose: verbose);
 }
 
 /// Check equivalence of resolution impact for [member1] and [member2].
 void checkImpacts(Compiler compiler1, Element member1,
                   Compiler compiler2, Element member2,
                   {bool verbose: false}) {
   ResolutionImpact impact1 = compiler1.resolution.getResolutionImpact(member1);
   ResolutionImpact impact2 =
       compiler2.serialization.deserializer.getResolutionImpact(member2);
 
   if (impact1 == null || impact2 == null) return;
 
   if (verbose) {
     print('Checking impacts for $member1 vs $member2');
   }
 
   testResolutionImpactEquivalence(impact1, impact2, const CheckStrategy());
 }