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

tools/testing/dart/multitest.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.
 
 #library("multitest");
 
+#import("dart:io");
+
 // Multitests are Dart test scripts containing lines of the form
 // " [some dart code] /// [key]: [error type]"
 //
 // For each key in the file, a new test file is made containing all
 // the normal lines of the file, and all of the multitest lines containing
 // that key, in the same order as in the source file.  The new test
 // is expected to fail if there is a non-empty error type listed, of
 // type 'compile-time error', 'runtime error', 'static type error', or
 // 'dynamic type error'.  The type error tests fail only in checked mode.
 // There is also a test created from only the untagged lines of the file,
@@ skipping 150 matching lines @@
   var split = testDir.split('/');
   var lastComponent = split.removeLast();
   Expect.isTrue(lastComponent == 'src');
   String path = '${generatedTestDir.path}/${split.last()}';
   Directory dir = new Directory(path);
   if (!dir.existsSync()) {
     dir.createSync();
   }
   return path;
 }