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

base/allocator/allocator_extension.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_EXTENSION_H
 #define BASE_ALLOCATOR_ALLOCATOR_EXTENSION_H
-#pragma once
 
 #include "base/allocator/allocator_extension_thunks.h"
 #include "base/base_export.h"
 #include "build/build_config.h"
 
 namespace base {
 namespace allocator {
 
 // Request that the allocator print a human-readable description of the current
 // state of the allocator into a null-terminated string in the memory segment
@@ skipping 18 matching lines @@
 // functions.
 BASE_EXPORT void SetGetStatsFunction(
     thunks::GetStatsFunction* get_stats_function);
 
 BASE_EXPORT void SetReleaseFreeMemoryFunction(
     thunks::ReleaseFreeMemoryFunction* release_free_memory_function);
 }  // namespace allocator
 }  // namespace base
 
 #endif