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

base/atomicops_internals_mips_gcc.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 file is an internal atomic implementation, use base/atomicops.h instead.
 //
 // LinuxKernelCmpxchg and Barrier_AtomicIncrement are from Google Gears.
 
 #ifndef BASE_ATOMICOPS_INTERNALS_MIPS_GCC_H_
 #define BASE_ATOMICOPS_INTERNALS_MIPS_GCC_H_
-#pragma once
 
 #define ATOMICOPS_COMPILER_BARRIER() __asm__ __volatile__("" : : : "memory")
 
 namespace base {
 namespace subtle {
 
 // Atomically execute:
 //      result = *ptr;
 //      if (*ptr == old_value)
 //        *ptr = new_value;
@@ skipping 131 matching lines @@
   MemoryBarrier();
   return *ptr;
 }
 
 } // namespace base::subtle
 } // namespace base
 
 #undef ATOMICOPS_COMPILER_BARRIER
 
 #endif  // BASE_ATOMICOPS_INTERNALS_MIPS_GCC_H_