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

tests/standalone/src/StreamPipeTest.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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 #library("StreamPipeTest");
+#import("dart:io");
 #source("TestingServer.dart");
 
 // Helper method to be able to run the test from the runtime
 // directory, or the top directory.
 String getDataFilename(String path) =>
     new File(path).existsSync() ? path : '../' + path;
 
 
 bool compareFileContent(String fileName1,
                         String fileName2,
@@ skipping 241 matching lines @@
   srcStream.pipe(dstStream, close: false);
 }
 
 
 main() {
   testFileToFilePipe1();
   testFileToFilePipe2();
   testFileToFilePipe3();
   PipeServerGame echoServerGame = new PipeServerGame.start();
 }