Fix DevFS writes with subdirectories

runtime/bin/vmservice/vmservice_io.dart

 // Copyright (c) 2013, 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 vmservice_io;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:io';
@@ skipping 54 matching lines @@
   Directory temp = await Directory.systemTemp.createTemp(base);
   return temp.uri;
 }
 
 Future deleteDirCallback(Uri path) async {
   Directory dir = new Directory.fromUri(path);
   await dir.delete(recursive: true);
 }
 
 Future writeFileCallback(Uri path, List<int> bytes) async {
-  var file = await new File.fromUri(path);
+  var file = new File.fromUri(path);
+  var parent_directory = file.parent;
+  await parent_directory.create(recursive: true);
   await file.writeAsBytes(bytes);
 }
 
 Future<List<int>> readFileCallback(Uri path) async {
-  var file = await new File.fromUri(path);
+  var file = new File.fromUri(path);
   return await file.readAsBytes();
 }
 
 Future<List<Map<String,String>>> listFilesCallback(Uri dirPath) async {
   var dir = new Directory.fromUri(dirPath);
   var dirPathStr = dirPath.path;
   var stream = dir.list(recursive: true);
   var result = [];
   await for (var fileEntity in stream) {
     var filePath = new Uri.file(fileEntity.path).path;
@@ skipping 62 matching lines @@
     Timer.run(() {});
   }
   scriptLoadPort.handler = _processLoadRequest;
   // Register signal handler after a small delay to avoid stalling main
   // isolate startup.
   _registerSignalHandlerTimer = new Timer(shortDelay, _registerSignalHandler);
   return scriptLoadPort;
 }
 
 _shutdown() native "VMServiceIO_Shutdown";