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

sdk/lib/io/io_resource_info.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.
 
-part of "dart:io";
+part of dart.io;
 
 abstract class _IOResourceInfo {
   final String type;
   final int id;
   String get name;
   static int _count = 0;
 
   static final Stopwatch _sw = new Stopwatch()..start();
   static final _startTime = new DateTime.now().millisecondsSinceEpoch;
 
@@ skipping 257 matching lines @@
   static SocketOpened(_SocketResourceInfo info) {
     assert(!openSockets.containsKey(info.id));
     openSockets[info.id] = info;
   }
 
   static SocketClosed(_SocketResourceInfo info) {
     assert(openSockets.containsKey(info.id));
     openSockets.remove(info.id);
   }
 }