dart:io | Add asynchronous versions of the methods of FileSystemEntity and Link.

runtime/bin/file.h

 // 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.
 
 #ifndef BIN_FILE_H_
 #define BIN_FILE_H_
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
@@ skipping 64 matching lines @@
     kLengthRequest = 10,
     kLengthFromPathRequest = 11,
     kLastModifiedRequest = 12,
     kFlushRequest = 13,
     kReadByteRequest = 14,
     kWriteByteRequest = 15,
     kReadRequest = 16,
     kReadIntoRequest = 17,
     kWriteFromRequest = 18,
     kCreateLinkRequest = 19,
-    kDeleteLinkRequest = 20
+    kDeleteLinkRequest = 20,
+    kLinkTargetRequest = 21
   };
 
   ~File();
 
   // Read/Write attempt to transfer num_bytes to/from buffer. It returns
   // the number of bytes read/written.
   int64_t Read(void* buffer, int64_t num_bytes);
   int64_t Write(const void* buffer, int64_t num_bytes);
 
   // ReadFully and WriteFully do attempt to transfer num_bytes to/from
@@ skipping 69 matching lines @@
 
   static NativeService file_service_;
 
   DISALLOW_COPY_AND_ASSIGN(File);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_FILE_H_