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

base/threading/non_thread_safe.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_THREADING_NON_THREAD_SAFE_H_
 #define BASE_THREADING_NON_THREAD_SAFE_H_
-#pragma once
 
 // Classes deriving from NonThreadSafe may need to suppress MSVC warning 4275:
 // non dll-interface class 'Bar' used as base for dll-interface class 'Foo'.
 // There is a specific macro to do it: NON_EXPORTED_BASE(), defined in
 // compiler_specific.h
 #include "base/compiler_specific.h"
 
 // See comment at top of thread_checker.h
 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
 #define ENABLE_NON_THREAD_SAFE 1
@@ skipping 49 matching lines @@
 #else
 class NonThreadSafe : public NonThreadSafeDoNothing {
 };
 #endif  // ENABLE_NON_THREAD_SAFE
 
 #undef ENABLE_NON_THREAD_SAFE
 
 }  // namespace base
 
 #endif  // BASE_NON_THREAD_SAFE_H_