Split serialization tests further

tests/compiler/dart2js/serialization/compilation_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_compilation_test;
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/filenames.dart';
 import '../memory_compiler.dart';
 import 'helper.dart';
 import 'test_data.dart';
 import '../output_collector.dart';
 
+/// Number of tests that are not part of the automatic test grouping.
+int SKIP_COUNT = 2;
+
+/// Number of groups that the [TESTS] are split into.
+int SPLIT_COUNT = 4;
+
 main(List<String> args) {
   asyncTest(() async {
     Arguments arguments = new Arguments.from(args);
     SerializedData serializedData =
         await serializeDartCore(arguments: arguments);
     if (arguments.filename != null) {
       Uri entryPoint = Uri.base.resolve(nativeToUriPath(arguments.filename));
       await compile(
           entryPoint,
           resolutionInputs: serializedData.toUris(),
@@ skipping 27 matching lines @@
         memorySourceFiles: sourceFiles,
         resolutionInputs: resolutionInputs,
         options: options,
         outputProvider: outputCollector);
   });
   if (verbose) {
     print(outputCollector.getOutput('', 'js'));
   }
 }