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

base/synchronization/condition_variable.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.
 
 // ConditionVariable wraps pthreads condition variable synchronization or, on
 // Windows, simulates it.  This functionality is very helpful for having
 // several threads wait for an event, as is common with a thread pool managed
 // by a master.  The meaning of such an event in the (worker) thread pool
 // scenario is that additional tasks are now available for processing.  It is
 // used in Chrome in the DNS prefetching system to notify worker threads that
@@ skipping 46 matching lines @@
 // Signal to revive.  Fairness would (if publicly supported) assure that the
 // thread that has Wait()ed the longest is selected. The default policy
 // may improve performance, as the selected thread may have a greater chance of
 // having some of its stack data in various CPU caches.
 //
 // For a discussion of the many very subtle implementation details, see the FAQ
 // at the end of condition_variable_win.cc.
 
 #ifndef BASE_SYNCHRONIZATION_CONDITION_VARIABLE_H_
 #define BASE_SYNCHRONIZATION_CONDITION_VARIABLE_H_
-#pragma once
 
 #include "build/build_config.h"
 
 #if defined(OS_POSIX)
 #include <pthread.h>
 #endif
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/synchronization/lock.h"
@@ skipping 32 matching lines @@
 #endif
 
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
 };
 
 }  // namespace base
 
 #endif  // BASE_SYNCHRONIZATION_CONDITION_VARIABLE_H_