Fix a number of editor errors and warnings in io tests

runtime/bin/file.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.
 
 
 /**
  * FileMode describes the modes in which a file can be opened.
  */
 class FileMode {
   static final READ = const FileMode._internal(0);
@@ skipping 101 matching lines @@
    * not truncated.
    */
   void open(FileMode mode, void callback(RandomAccessFile opened));
 
   /**
    * Synchronously open the file for random access operations. The
    * result is a RandomAccessFile on which random access operations
    * can be performed. Opened RandomAccessFiles must be closed using
    * the [close] method.
    *
-   * See [open] for information on the [:mode:] argument.
+   * The default value for [mode] is [:FileMode.READ:].
+   *
+   * See [open] for information on the [mode] argument.
    */
-  RandomAccessFile openSync(FileMode mode);
+  RandomAccessFile openSync([FileMode mode]);
 
   /**
    * Get the canonical full path corresponding to the file name.  The
    * callback is called with the result when the
    * fullPath operation completes. If the operation fails the
    * [onError] function registered on the file object is called.
    */
   void fullPath(void callback(String path));
 
   /**
@@ skipping 255 matching lines @@
         sb.add(" ($osError)");
       }
     } else if (osError != null) {
       sb.add(": osError");
     }
     return sb.toString();
   }
   final String message;
   final OSError osError;
 }