Make the temporary OSError allocation method private.

runtime/bin/common.dart

 // 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.
 
 /**
   * An [OSError] object holds information about an error from the
   * operating system.
   */
 class OSError {
   static final int noErrorCode = -1;
@@ skipping 24 matching lines @@
   final String message;
 
   /**
     * Error code supplied by the operating system. Will have the value
     * [noErrorCode] if there is no error code associated with the error.
     */
   final int errorCode;
 }
 
 
-/**
-  * Utility for creating an OSError instance. NOTE: This will go away
-  * soon, so please don't use this utility function. The reason for
-  * having it temporarily is that the Dart C API does not currently
-  * support constructing objects.
-  */
 // TODO(sgjesse): Remove this once Dart constructors can be invoked
 // through the API.
-class IOUtils {
-  static OSError makeOSError(message, code) => new OSError(message, code);
-}
+OSError _makeOSError(message, code) => new OSError(message, code);