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

sdk/lib/io/io_service.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.
 
-part of "dart:io";
+part of dart.io;
 
 // This list must be kept in sync with the list in runtime/bin/io_service.h
 const int _FILE_EXISTS = 0;
 const int _FILE_CREATE = 1;
 const int _FILE_DELETE = 2;
 const int _FILE_RENAME = 3;
 const int _FILE_COPY = 4;
 const int _FILE_OPEN = 5;
 const int _FILE_RESOLVE_SYMBOLIC_LINKS = 6;
 const int _FILE_CLOSE = 7;
@@ skipping 29 matching lines @@
 const int _DIRECTORY_CREATE_TEMP = 37;
 const int _DIRECTORY_LIST_START = 38;
 const int _DIRECTORY_LIST_NEXT = 39;
 const int _DIRECTORY_LIST_STOP = 40;
 const int _DIRECTORY_RENAME = 41;
 const int _SSL_PROCESS_FILTER = 42;
 
 class _IOService {
   external static Future _dispatch(int request, List data);
 }