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

tests/standalone/src/ProcessStderrTest.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 process communication.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 #library("ProcessStderrTest");
+#import("dart:io");
 #source("ProcessTestUtil.dart");
 
 void test(Process process, int expectedExitCode) {
   // Wait for the process to start and then interact with it.
   process.startHandler = () {
     List<int> data = "ABCDEFGHI\n".charCodes();
     final int dataSize = data.length;
 
     InputStream input = process.stderr;
     OutputStream output = process.stdin;
@@ skipping 39 matching lines @@
 
   // Run the test using the dart binary with an echo script.
   // The test runner can be run from either the root or from runtime.
   var scriptFile = new File("tests/standalone/src/ProcessStdIOScript.dart");
   if (!scriptFile.existsSync()) {
     scriptFile = new File("../tests/standalone/src/ProcessStdIOScript.dart");
   }
   Expect.isTrue(scriptFile.existsSync());
   test(new Process.start(getDartFileName(), [scriptFile.name, "1"]), 0);
 }