Refactor unittests

tests/compiler/dart2js/serialization/test_data.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_data;
 
 const List<Test> TESTS = const <Test>[
   const Test(const {
     'main.dart': 'main() {}'
   }),
@@ skipping 198 matching lines @@
   final int expectedWarningCount;
   final int expectedHintCount;
   final int expectedInfoCount;
 
   const Test(this.sourceFiles, {
     this.expectedErrorCount: 0,
     this.expectedWarningCount: 0,
     this.expectedHintCount: 0,
     this.expectedInfoCount: 0});
 }