Refactor unittests

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 '../memory_compiler.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common/resolution.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/constants/constructors.dart';
 import 'package:compiler/src/constants/expressions.dart';
 import 'package:compiler/src/dart_types.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/diagnostics/invariant.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/visitor.dart';
@@ skipping 354 matching lines @@
 
   if (impact1 == null) {
     throw 'Missing impact for $member1. $member2 has $impact2';
   }
   if (impact2 == null) {
     throw 'Missing impact for $member2. $member1 has $impact1';
   }
 
   testResolutionImpactEquivalence(impact1, impact2, const CheckStrategy());
 }