fix #27771, create directory if needed

pkg/dev_compiler/test/worker/worker_test.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.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:bazel_worker/bazel_worker.dart';
 // TODO(jakemac): Remove once this is a part of the testing library.
 import 'package:bazel_worker/src/async_message_grouper.dart';
 import 'package:bazel_worker/testing.dart';
 import 'package:test/test.dart';
 
 main() {
   group('Hello World', () {
     final argsFile = new File('test/worker/hello_world.args').absolute;
     final inputDartFile = new File('test/worker/hello_world.dart').absolute;
-    final outputJsFile = new File('test/worker/hello_world.js').absolute;
+    final outputJsFile = new File('test/worker/out/hello_world.js').absolute;
     final dartSdkSummary = new File('lib/sdk/ddc_sdk.sum').absolute;
     final executableArgs = ['bin/dartdevc.dart'];
     final compilerArgs = [
       '--no-source-map',
       '--no-summarize',
       '--dart-sdk-summary',
       dartSdkSummary.path,
       '-o',
       outputJsFile.path,
       inputDartFile.path,
     ];
 
     setUp(() {
       inputDartFile.createSync();
       inputDartFile.writeAsStringSync('main() => print("hello world");');
     });
 
     tearDown(() {
       if (inputDartFile.existsSync()) inputDartFile.deleteSync();
-      if (outputJsFile.existsSync()) outputJsFile.deleteSync();
+      if (outputJsFile.parent.existsSync()) {
+        outputJsFile.parent.deleteSync(recursive: true);

[kevmoo, 2016/11/08 02:51:30]

Huh? This seems – bad.

Are we sure this directory is empty?

[Jennifer Messerly, 2016/11/08 18:11:51]

it's a test folder, so yes (we're in "worker_test.dart"). I'm happy to make it
more defensive somehow, if you have suggestions.

[kevmoo, 2016/11/08 18:16:47]

*sigh* Sorry. Paranoid. :-)

+      }
       if (argsFile.existsSync()) argsFile.deleteSync();
     });
 
     test('can compile in worker mode', () async {
       var args = executableArgs.toList()..add('--persistent_worker');
       var process = await Process.start('dart', args);
       var messageGrouper = new AsyncMessageGrouper(process.stdout);
 
       var request = new WorkRequest();
       request.arguments.addAll(compilerArgs);
@@ skipping 218 matching lines @@
 Future<WorkResponse> _readResponse(MessageGrouper messageGrouper) async {
   var buffer = (await messageGrouper.next) as List<int>;
   try {
     return new WorkResponse.fromBuffer(buffer);
   } catch (_) {
     var bufferAsString =
         buffer == null ? '' : 'String: ${UTF8.decode(buffer)}\n';
     throw 'Failed to parse response:\nbytes: $buffer\n$bufferAsString';
   }
 }