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

base/threading/non_thread_safe_impl.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_IMPL_H_
 #define BASE_THREADING_NON_THREAD_SAFE_IMPL_H_
-#pragma once
 
 #include "base/base_export.h"
 #include "base/threading/thread_checker_impl.h"
 
 namespace base {
 
 // Full implementation of NonThreadSafe, for debug mode or for occasional
 // temporary use in release mode e.g. when you need to CHECK on a thread
 // bug that only occurs in the wild.
 //
@@ skipping 13 matching lines @@
   // used exclusively on another thread.
   void DetachFromThread();
 
  private:
   ThreadCheckerImpl thread_checker_;
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_NON_THREAD_SAFE_IMPL_H_