Show actualy FD for files in Observatory.

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 55 matching lines @@
     kCreatedTime = 1,
     kModifiedTime = 2,
     kAccessedTime = 3,
     kMode = 4,
     kSize = 5,
     kStatSize = 6
   };
 
   ~File();
 
+  intptr_t GetFD();
+
   // 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
   // the buffer. In the event of short accesses they will loop internally until
   // the whole buffer has been transferred or an error occurs. If an error
   // occurred the result will be set to false.
   bool ReadFully(void* buffer, int64_t num_bytes);
@@ skipping 92 matching lines @@
   // 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);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_FILE_H_