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

base/win/event_trace_provider.h

 // Copyright (c) 2011 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.
 //
 // Declaration of a Windows event trace provider class, to allow using
 // Windows Event Tracing for logging transport and control.
 #ifndef BASE_WIN_EVENT_TRACE_PROVIDER_H_
 #define BASE_WIN_EVENT_TRACE_PROVIDER_H_
-#pragma once
 
 #include <windows.h>
 #include <wmistr.h>
 #include <evntrace.h>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 
 namespace base {
 namespace win {
@@ skipping 147 matching lines @@
   // RegisterTraceGuids. Non-const, because that's how the API needs it.
   static TRACE_GUID_REGISTRATION obligatory_guid_registration_;
 
   DISALLOW_COPY_AND_ASSIGN(EtwTraceProvider);
 };
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_WIN_EVENT_TRACE_PROVIDER_H_