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

frog/file_system_vm.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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('file_system_vm');
+#import('dart:io');
 #import('file_system.dart');
 
 /** File system implementation using the vm api's. */
 class VMFileSystem implements FileSystem {
   void writeString(String outfile, String text) {
     var f = new File(outfile);
     var stream = f.openOutputStream();
     stream.write(text.charCodes());
     stream.close();
   }
@@ skipping 14 matching lines @@
   void createDirectory(String path, [bool recursive = false]) {
     // TODO(rnystrom): Implement.
     throw 'createDirectory() is not implemented by VMFileSystem yet.';
   }
 
   void removeDirectory(String path, [bool recursive = false]) {
     // TODO(rnystrom): Implement.
     throw 'removeDirectory() is not implemented by VMFileSystem yet.';
   }
 }