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

base/command_line.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 class works with command lines: building and parsing.
 // Arguments with prefixes ('--', '-', and on Windows, '/') are switches.
 // Switches will precede all other arguments without switch prefixes.
 // Switches can optionally have values, delimited by '=', e.g., "-switch=value".
 // An argument of "--" will terminate switch parsing during initialization,
 // interpreting subsequent tokens as non-switch arguments, regardless of prefix.
 
 // There is a singleton read-only CommandLine that represents the command line
 // that the current process was started with.  It must be initialized in main().
 
 #ifndef BASE_COMMAND_LINE_H_
 #define BASE_COMMAND_LINE_H_
-#pragma once
 
 #include <stddef.h>
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "build/build_config.h"
 
 class FilePath;
@@ skipping 130 matching lines @@
   StringVector argv_;
 
   // Parsed-out switch keys and values.
   SwitchMap switches_;
 
   // The index after the program and switches, any arguments start here.
   size_t begin_args_;
 };
 
 #endif  // BASE_COMMAND_LINE_H_