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

base/global_descriptors_posix.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.
 
 #ifndef BASE_GLOBAL_DESCRIPTORS_POSIX_H_
 #define BASE_GLOBAL_DESCRIPTORS_POSIX_H_
-#pragma once
 
 #include "build/build_config.h"
 
 #include <vector>
 #include <utility>
 
 #include <stdint.h>
 
 #include "base/memory/singleton.h"
 
@@ skipping 44 matching lines @@
   friend struct DefaultSingletonTraits<GlobalDescriptors>;
   GlobalDescriptors();
   ~GlobalDescriptors();
 
   Mapping descriptors_;
 };
 
 }  // namespace base
 
 #endif  // BASE_GLOBAL_DESCRIPTORS_POSIX_H_