Use relative URIs for core library part-of statements.

sdk/lib/io/stdio.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 "io.dart";
 
 const int _STDIO_HANDLE_TYPE_TERMINAL = 0;
 const int _STDIO_HANDLE_TYPE_PIPE = 1;
 const int _STDIO_HANDLE_TYPE_FILE = 2;
 const int _STDIO_HANDLE_TYPE_SOCKET = 3;
 const int _STDIO_HANDLE_TYPE_OTHER = 4;
 
 class _StdStream extends Stream<List<int>> {
   final Stream<List<int>> _stream;
 
@@ skipping 406 matching lines @@
 }
 
 class _StdIOUtils {
   external static _getStdioOutputStream(int fd);
   external static Stdin _getStdioInputStream();
 
   /// Returns the socket type or `null` if [socket] is not a builtin socket.
   external static int _socketType(Socket socket);
   external static _getStdioHandleType(int fd);
 }