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

base/win/event_trace_controller.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 controller class.
 // The controller takes care of creating and manipulating event trace
 // sessions.
 //
 // Event tracing for Windows is a system-provided service that provides
 // logging control and high-performance transport for generic, binary trace
 // events. Event trace providers register with the system by their name,
 // which is a GUID, and can from that point forward receive callbacks that
 // start or end tracing and that change their trace level and enable mask.
 //
 // A trace controller can create an event tracing session, which either
 // sends events to a binary file, or to a realtime consumer, or both.
 //
 // A trace consumer consumes events from zero or one realtime session,
 // as well as potentially from multiple binary trace files.
 #ifndef BASE_WIN_EVENT_TRACE_CONTROLLER_H_
 #define BASE_WIN_EVENT_TRACE_CONTROLLER_H_
-#pragma once
 
 #include <windows.h>
 #include <wmistr.h>
 #include <evntrace.h>
 #include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 
 namespace base {
@@ skipping 110 matching lines @@
   std::wstring session_name_;
   TRACEHANDLE session_;
 
   DISALLOW_COPY_AND_ASSIGN(EtwTraceController);
 };
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_WIN_EVENT_TRACE_CONTROLLER_H_