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

base/debug/trace_event.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 header is designed to give you trace_event macros without specifying
 // how the events actually get collected and stored. If you need to expose trace
 // event to some other universe, you can copy-and-paste this file,
 // implement the TRACE_EVENT_API macros, and do any other necessary fixup for
 // the target platform. The end result is that multiple libraries can funnel
 // events through to a shared trace event collector.
@@ skipping 132 matching lines @@
 // because AddTraceEvent is threadsafe internally and checks the enabled state
 // again under lock.
 //
 // Without the use of these static category pointers and enabled flags all
 // trace points would carry a significant performance cost of aquiring a lock
 // and resolving the category.
 
 
 #ifndef BASE_DEBUG_TRACE_EVENT_H_
 #define BASE_DEBUG_TRACE_EVENT_H_
-#pragma once
 
 #include <string>
 
 #include "base/atomicops.h"
 #include "base/debug/trace_event_impl.h"
 #include "build/build_config.h"
 
 // By default, const char* argument values are assumed to have long-lived scope
 // and will not be copied. Use this macro to force a const char* to be copied.
 #define TRACE_STR_COPY(str) \
@@ skipping 699 matching lines @@
     const char* name;
     int threshold_begin_id;
   };
   Data* p_data_;
   Data data_;
 };
 
 }  // namespace trace_event_internal
 
 #endif  // BASE_DEBUG_TRACE_EVENT_H_