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

base/debug/trace_event_win.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 the Windows-specific declarations for trace_event.h.
 #ifndef BASE_DEBUG_TRACE_EVENT_WIN_H_
 #define BASE_DEBUG_TRACE_EVENT_WIN_H_
-#pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/debug/trace_event.h"
 #include "base/win/event_trace_provider.h"
 
 // Fwd.
 template <typename Type>
 struct StaticMemorySingletonTraits;
@@ skipping 96 matching lines @@
 // The "name" string as a zero-terminated ASCII string.
 // The id pointer in the machine bitness.
 // The "extra" string as a zero-terminated ASCII string.
 // Optionally the stack trace, consisting of a DWORD "depth", followed
 //    by an array of void* (machine bitness) of length "depth".
 
 }  // namespace debug
 }  // namespace base
 
 #endif  // BASE_DEBUG_TRACE_EVENT_WIN_H_