Implement File.directory() and File.directorySync() to get

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_
 
 #if defined(_WIN32)
 typedef signed __int64 int64_t;
 typedef unsigned __int8 uint8_t;
@@ skipping 70 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* name);
   static bool Create(const char* name);
   static bool Delete(const char* name);
   static bool IsAbsolutePath(const char* pathname);
   static char* GetCanonicalPath(const char* name);
+  static char* GetContainingDirectory(char* name);
   static const char* PathSeparator();
   static const char* StringEscapedPathSeparator();
   static StdioHandleType GetStdioHandleType(int fd);
 
  private:
   File(const char* name, FileHandle* handle) : name_(name), handle_(handle) { }
   void Close();
   bool IsClosed();
 
   static const int kClosedFd = -1;
 
   const char* name_;
   // FileHandle is an OS specific class which stores data about the file.
   FileHandle* handle_;  // OS specific handle for the file.
 
   // DISALLOW_COPY_AND_ASSIGN(File).
   File(const File&);
   void operator=(const File&);
 };
 
 #endif  // BIN_FILE_H_