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

tests/standalone/src/ProcessBrokenPipe.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.
-//
-// Process test program to test closed stdin from child process.
-
-#source("ProcessTestUtil.dart");
-
-main() {
-  // Running dart without arguments makes it close right away.
-  Process process = new Process.start(getDartBinFileName(), []);
-
-  // Write to the stdin after the process is terminated to test
-  // writing to a broken pipe.
-  process.exitHandler = (code) {
-    Expect.isFalse(process.stdin.write([0]));
-    process.close();
-  };
-}