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

base/callback_internal.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 contains utility functions and classes that help the
 // implementation, and management of the Callback objects.
 
 #ifndef BASE_CALLBACK_INTERNAL_H_
 #define BASE_CALLBACK_INTERNAL_H_
-#pragma once
 
 #include <stddef.h>
 
 #include "base/base_export.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 
 template <typename T>
 class ScopedVector;
 
@@ skipping 164 matching lines @@
   return p.Pass();
 }
 
 template <typename T>
 ScopedVector<T> CallbackForward(ScopedVector<T>& p) { return p.Pass(); }
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_CALLBACK_INTERNAL_H_