Fix errors in previous commit

sdk/lib/io/file_impl.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;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 
@@ skipping 679 matching lines @@
     return result;
   }
 
   Future<int> readInto(List<int> buffer, [int start = 0, int end]) {
     if (buffer is !List ||
         (start != null && start is !int) ||
         (end != null && end is !int)) {
       throw new ArgumentError();
     }
     end = RangeError.checkValidRange(start, end, buffer.length);
-    if (end == start) return 0;
+    if (end == start) return new Future.value(0);
     int length = end - start;
     return _dispatch(_FILE_READ_INTO, [_id, length]).then((response) {
       if (_isErrorResponse(response)) {
         throw _exceptionFromResponse(response, "readInto failed", path);
       }
       var read = response[1];
       var data = response[2];
       buffer.setRange(start, start + read, data);
       _readCount++;
       _totalRead += read;
@@ skipping 52 matching lines @@
   }
 
   Future<RandomAccessFile> writeFrom(
       List<int> buffer, [int start = 0, int end]) {
     if ((buffer is !List) ||
         (start != null && start is !int) ||
         (end != null && end is !int)) {
       throw new ArgumentError("Invalid arguments to writeFrom");
     }
     end = RangeError.checkValidRange(start, end, buffer.length);
-    if (end == start) return;
+    if (end == start) return new Future.value(this);
     _BufferAndStart result;
     try {
       result = _ensureFastAndSerializableByteData(buffer, start, end);
     } catch (e) {
       return new Future.error(e);
     }
 
     List request = new List(4);
     request[0] = _id;
     request[1] = result.buffer;
@@ skipping 254 matching lines @@
   void _checkAvailable() {
     if (_asyncDispatched) {
       throw new FileSystemException("An async operation is currently pending",
                                     path);
     }
     if (closed) {
       throw new FileSystemException("File closed", path);
     }
   }
 }