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

sdk/lib/io/directory_impl.dart

 // Copyright (c) 2012, 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;
 
 class _Directory extends FileSystemEntity implements Directory {
   final String path;
 
   _Directory(this.path) {
     if (path is! String) {
       throw new ArgumentError('${Error.safeToString(path)} '
           'is not a String');
     }
   }
@@ skipping 365 matching lines @@
           responseError[_OSERROR_RESPONSE_ERROR_CODE]);
       var errorPath = message[RESPONSE_PATH];
       if (errorPath == null) errorPath = path;
       controller.addError(
           new FileSystemException("Directory listing failed", errorPath, err));
     } else {
       controller.addError(new FileSystemException("Internal error"));
     }
   }
 }