Remove #pragma once. Just from base/ for now.

base/file_descriptor_posix.h

 // Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_FILE_DESCRIPTOR_POSIX_H_
 #define BASE_FILE_DESCRIPTOR_POSIX_H_
-#pragma once
 
 namespace base {
 
 // -----------------------------------------------------------------------------
 // We introduct a special structure for file descriptors in order that we are
 // able to use template specialisation to special-case their handling.
 //
 // WARNING: (Chromium only) There are subtleties to consider if serialising
 // these objects over IPC. See comments in ipc/ipc_message_utils.h
 // above the template specialisation for this structure.
@@ skipping 19 matching lines @@
   int fd;
   // If true, this file descriptor should be closed after it has been used. For
   // example an IPC system might interpret this flag as indicating that the
   // file descriptor it has been given should be closed after use.
   bool auto_close;
 };
 
 }  // namespace base
 
 #endif  // BASE_FILE_DESCRIPTOR_POSIX_H_