dart:io | Add Link.targetSync on all platforms.

runtime/bin/file.h

 // 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.
 
 #ifndef BIN_FILE_H_
 #define BIN_FILE_H_
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
@@ skipping 109 matching lines @@
   // Create a file object for the specified stdio file descriptor
   // (stdin, stout or stderr).
   static File* OpenStdio(int fd);
 
   static bool Exists(const char* path);
   static bool Create(const char* path);
   static bool CreateLink(const char* path, const char* target);
   static bool Delete(const char* path);
   static off_t LengthFromPath(const char* path);
   static time_t LastModified(const char* path);
+  static char* LinkTarget(const char* pathname);
   static bool IsAbsolutePath(const char* path);
   static char* GetCanonicalPath(const char* path);
   static char* GetContainingDirectory(char* path);
   static const char* PathSeparator();
   static const char* StringEscapedPathSeparator();
   static Type GetType(const char* path, bool follow_links);
   static StdioHandleType GetStdioHandleType(int fd);
 
   static FileOpenMode DartModeToFileMode(DartFileOpenMode mode);
 
   static Dart_Port GetServicePort();
 
  private:
   explicit File(FileHandle* handle) : handle_(handle) { }
   void Close();
 
   static const int kClosedFd = -1;
 
   // FileHandle is an OS specific class which stores data about the file.
   FileHandle* handle_;  // OS specific handle for the file.
 
   static NativeService file_service_;
 
   DISALLOW_COPY_AND_ASSIGN(File);
 };
 
 #endif  // BIN_FILE_H_