Add error handling to random access file

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 208 matching lines @@
    */
   void close(void callback());
 
   /**
    * Synchronously close the file.
    */
   void closeSync();
 
   /**
    * Read a byte from the file. When the byte has been read the
-   * callback is called with the value.
+   * callback is called with the value. If end of file has been
+   * reached the value will be -1.
    */
   void readByte(void callback(int byte));
 
   /**
-   * Synchronously read a single byte from the file.
+   * Synchronously read a single byte from the file. If end of file
+   * has been reached -1 is returned.
    */
   int readByteSync();
 
   /**
    * Read a List<int> from the file. When the list has been read the
    * callback is called with an integer indicating how much was read.
    */
   void readList(List<int> buffer, int offset, int bytes,
                 void callback(int read));
 
@@ skipping 109 matching lines @@
   /**
    * Sets the handler that gets called when there are no more write
    * operations pending for this file.
    */
   void set onNoPendingWrites(void handler());
 
   /**
    * Sets the handler that gets called when errors occur when
    * operating on this file.
    */
-  void set onError(void handler(String error));
+  void set onError(void handler(Exception e));
 }
 
 
 class FileIOException implements Exception {
   const FileIOException([String this.message = "",
                          OSError this.osError = null]);
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.add("FileIOException");
     if (!message.isEmpty()) {
       sb.add(": $message");
       if (osError != null) {
         sb.add(" ($osError)");
       }
     } else if (osError != null) {
       sb.add(": osError");
     }
     return sb.toString();
   }
   final String message;
   final OSError osError;
 }