Add test of unittests.

tests/compiler/dart2js/inference_stats_test.dart

 // Copyright (c) 2015, 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.
 // SharedOptions=-Dsend_stats=true
 
 /// Tests that we compute send metrics correctly in many simple scenarios.
 library dart2js.test.send_measurements_test;
 
 import 'dart:async';
 import 'package:test/test.dart';
 import 'package:dart2js_info/info.dart';
+import 'package:dart2js_info/src/util.dart' show
+    recursiveDiagnosticString;
 import 'memory_compiler.dart';
-import 'dart:io';
 
 main() {
   test('nothing is reachable, nothing to count', () {
     return _check('''
       main() {}
       test() { int x = 3; }
       ''');
   });
 
   test('local variable read', () {
@@ skipping 306 matching lines @@
 }
 
 /// Helper that runs the compiler and returns the [GlobalResult] computed for
 /// it.
 Future<AllInfo> _compileAndGetStats(String program) async {
   var result = await runCompiler(
       memorySourceFiles: {'main.dart': program}, options: ['--dump-info']);
   expect(result.compiler.compilationFailed, isFalse);
   return result.compiler.dumpInfoTask.infoCollector.result;
 }