Split dart:builtin into dart:builtin and dart:io.

tests/standalone/src/ProcessStdIOScript.dart

 // Copyright (c) 2011, 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.
 //
 // Utility script to echo stdin to stdout or stderr or both.
 
+#import("dart:io");
+
 main() {
   var options = new Options();
   if (options.arguments.length > 0) {
     if (options.arguments[0] == "0") {
       stdin.dataHandler = () => stdout.write(stdin.read());
     } else if (options.arguments[0] == "1") {
       stdin.dataHandler = () => stderr.write(stdin.read());
     } else if (options.arguments[0] == "2") {
       stdin.dataHandler = () {
         var data = stdin.read();
         stdout.write(data);
         stderr.write(data);
       };
     }
   }
 }