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

sdk/lib/io/string_transformer.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;
 
 /// The current system encoding.
 ///
 /// This us used for converting from bytes to/from String when
 /// communicating on stdin, stdout and stderr.
 ///
 /// On Windows this will use the currently active code page for the
 /// conversion. On all other systems it will always use UTF-8.
 const SystemEncoding SYSTEM_ENCODING = const SystemEncoding();
 
@@ skipping 102 matching lines @@
   _WindowsCodePageDecoderSink(this._sink);
 
   void close() {
     _sink.close();
   }
 
   void add(List<int> bytes) {
     _sink.add(_WindowsCodePageDecoder._decodeBytes(bytes));
   }
 }