Show actualy FD for files in Observatory.

runtime/bin/builtin_natives.cc

 // 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.
 
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 
 #include "include/dart_api.h"
 
@@ skipping 17 matching lines @@
   V(Directory_Create, 1)                                                       \
   V(Directory_Current, 0)                                                      \
   V(Directory_SetCurrent, 1)                                                   \
   V(Directory_SystemTemp, 0)                                                   \
   V(Directory_CreateTemp, 1)                                                   \
   V(Directory_Delete, 2)                                                       \
   V(Directory_Rename, 2)                                                       \
   V(Directory_List, 3)                                                         \
   V(File_Open, 2)                                                              \
   V(File_Exists, 1)                                                            \
+  V(File_GetFD, 1)                                                             \
   V(File_Close, 1)                                                             \
   V(File_ReadByte, 1)                                                          \
   V(File_WriteByte, 2)                                                         \
   V(File_Read, 2)                                                              \
   V(File_ReadInto, 4)                                                          \
   V(File_WriteFrom, 4)                                                         \
   V(File_Position, 1)                                                          \
   V(File_SetPosition, 2)                                                       \
   V(File_Truncate, 2)                                                          \
   V(File_Length, 1)                                                            \
@@ skipping 83 matching lines @@
   } else {
     // Uses fwrite to support printing NUL bytes.
     fwrite(chars, 1, length, stdout);
     fputs("\n", stdout);
   }
   fflush(stdout);
 }
 
 }  // namespace bin
 }  // namespace dart