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

base/files/file_path_watcher.h

 // Copyright (c) 2012 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.
 
 // This module provides a way to monitor a file or directory for changes.
 
 #ifndef BASE_FILES_FILE_PATH_WATCHER_H_
 #define BASE_FILES_FILE_PATH_WATCHER_H_
-#pragma once
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop_proxy.h"
 
 namespace base {
 namespace files {
@@ skipping 107 matching lines @@
  private:
   scoped_refptr<PlatformDelegate> impl_;
 
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 };
 
 }  // namespace files
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_PATH_WATCHER_H_