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

base/atomicops_internals_x86_gcc.h

 // Copyright (c) 2011 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 file is an internal atomic implementation, use base/atomicops.h instead.
 
 #ifndef BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
 #define BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
-#pragma once
 
 #include "base/base_export.h"
 
 // This struct is not part of the public API of this module; clients may not
 // use it.  (However, it's exported via BASE_EXPORT because clients implicitly
 // do use it at link time by inlining these functions.)
 // Features of this x86.  Values may not be correct before main() is run,
 // but are set conservatively.
 struct AtomicOps_x86CPUFeatureStruct {
   bool has_amd_lock_mb_bug; // Processor has AMD memory-barrier bug; do lfence
@@ skipping 241 matching lines @@
 }
 
 #endif  // defined(__x86_64__)
 
 } // namespace base::subtle
 } // namespace base
 
 #undef ATOMICOPS_COMPILER_BARRIER
 
 #endif  // BASE_ATOMICOPS_INTERNALS_X86_GCC_H_