Add 'start' and 'end' optional arguments to File.openRead(). This makes it possible to stream a sub…

sdk/lib/io/file.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;
 
 /**
  * FileMode describes the modes in which a file can be opened.
  */
 class FileMode {
@@ skipping 162 matching lines @@
   Future<String> fullPath();
 
   /**
    * Synchronously get the canonical full path corresponding to the file path.
    *
    * Throws a [FileIOException] if the operation fails.
    */
   String fullPathSync();
 
   /**
-   * Create a new independent [Stream](../dart_async/Stream.html) for the
-   * contents of this file.
+   * Create a new independent [Stream] for the contents of this file.
+   *
+   * If [start] is present, the file will be read from byte-offset [start].
+   * Otherwise from the beginning (index 0).
+   *
+   * If [end] is present, only up to byte-index [end] will be read. Otherwise,
+   * until end of file.
    *
    * In order to make sure that system resources are freed, the stream
    * must be read to completion or the subscription on the stream must
    * be cancelled.
    */
-  Stream<List<int>> openRead();
+  Stream<List<int>> openRead([int start, int end]);
 
   /**
    * Creates a new independent [IOSink] for the file. The
    * [IOSink] must be closed when no longer used, to free
    * system resources.
    *
    * An [IOSink] for a file can be opened in two modes:
    *
    * * [FileMode.WRITE]: truncates the file to length zero.
    * * [FileMode.APPEND]: sets the initial write position to the end
@@ skipping 332 matching lines @@
         sb.write(" ($osError)");
       }
     } else if (osError != null) {
       sb.write(": osError");
     }
     return sb.toString();
   }
   final String message;
   final OSError osError;
 }