Revert "Change some platform libraries to use `part of URI`."

sdk/lib/io/service_object.dart

 // Copyright (c) 2014, 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.
 
-part of "dart:io";
+part of dart.io;
 
 int _nextServiceId = 1;
 
 // TODO(ajohnsen): Use other way of getting a uniq id.
 abstract class _ServiceObject {
   int __serviceId = 0;
   int get _serviceId {
     if (__serviceId == 0) __serviceId = _nextServiceId++;
     return __serviceId;
   }
 
   Map _toJSON(bool ref);
 
   String get _servicePath => "$_serviceTypePath/$_serviceId";
 
   String get _serviceTypePath;
 
   String get _serviceTypeName;
 
   String _serviceType(bool ref) {
     if (ref) return "@$_serviceTypeName";
     return _serviceTypeName;
   }
 }