Add missing method to link.dart.

sdk/lib/io/link.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 /**
  * [Link] objects are references to filesystem links.
  *
  */
@@ skipping 189 matching lines @@
 
   bool _isErrorResponse(response) {
     return response is List && response[0] != _SUCCESS_RESPONSE;
   }
 
   void _ensureFileService() {
     if (_fileService == null) {
       _fileService = _FileUtils._newServicePort();
     }
   }
+
+  _exceptionFromResponse(response, String message) {
+    assert(_isErrorResponse(response));
+    switch (response[_ERROR_RESPONSE_ERROR_TYPE]) {
+      case _ILLEGAL_ARGUMENT_RESPONSE:
+        return new ArgumentError();
+      case _OSERROR_RESPONSE:
+        var err = new OSError(response[_OSERROR_RESPONSE_MESSAGE],
+                              response[_OSERROR_RESPONSE_ERROR_CODE]);
+        return new FileIOException(message, err);
+      case _FILE_CLOSED_RESPONSE:
+        return new FileIOException("File closed");
+      default:
+        return new Exception("Unknown error");
+    }
+  }
 }
 
 
 class LinkIOException implements Exception {
   const LinkIOException([String this.message = "",
                          String this.path = "",
                          OSError this.osError = null]);
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write("LinkIOException");
@@ skipping 10 matching lines @@
       if (path != null) {
         sb.write(", path = $path");
       }
     }
     return sb.toString();
   }
   final String message;
   final String path;
   final OSError osError;
 }