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

base/allocator/allocator_extension_thunks.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_ALLOCATOR_ALLOCATOR_THUNKS_EXTENSION_H
 #define BASE_ALLOCATOR_ALLOCATOR_THUNKS_EXTENSION_H
-#pragma once
 
 namespace base {
 namespace allocator {
 namespace thunks {
 
 // WARNING: You probably don't want to use this file unless you are routing a
 // new allocator extension from a specific allocator implementation to base.
 // See allocator_extension.h to see the interface that base exports.
 
 typedef void GetStatsFunction(char*, int);
 void SetGetStatsFunction(GetStatsFunction* get_stats_function);
 GetStatsFunction* GetGetStatsFunction();
 
 typedef void ReleaseFreeMemoryFunction();
 void SetReleaseFreeMemoryFunction(
     ReleaseFreeMemoryFunction* release_free_memory_function);
 ReleaseFreeMemoryFunction* GetReleaseFreeMemoryFunction();
 
 }  // namespace thunks
 }  // namespace allocator
 }  // namespace base
 
 #endif