Fix some analyzer warnings in dart:io.

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 328 matching lines @@
 
   external static _renameLink(String oldPath, String newPath);
 
   File renameSync(String newPath) {
     var result = _rename(path, newPath);
     throwIfError(result, "Cannot rename file to '$newPath'", path);
     return new File(newPath);
   }
 
   Directory get directory {
-    Path path = new Path(path).directoryPath;
+    Path path = new Path(this.path).directoryPath;
     return new Directory.fromPath(path);
   }
 
   Future<RandomAccessFile> open({FileMode mode: FileMode.READ}) {
     _ensureFileService();
     if (mode != FileMode.READ &&
         mode != FileMode.WRITE &&
         mode != FileMode.APPEND) {
       return new Future.error(new ArgumentError());
     }
@@ skipping 620 matching lines @@
   void _checkNotClosed() {
     if (closed) {
       throw new FileException("File closed", path);
     }
   }
 
   Future _closedException() {
     return new Future.error(new FileException("File closed", path));
   }
 }