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

base/threading/watchdog.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.
 
 // The Watchdog class creates a second thread that can Alarm if a specific
 // duration of time passes without proper attention.  The duration of time is
 // specified at construction time.  The Watchdog may be used many times by
 // simply calling Arm() (to start timing) and Disarm() (to reset the timer).
 // The Watchdog is typically used under a debugger, where the stack traces on
 // other threads can be examined if/when the Watchdog alarms.
 
 // Some watchdogs will be enabled or disabled via command line switches. To
 // facilitate such code, an "enabled" argument for the constuctor can be used
 // to permanently disable the watchdog.  Disabled watchdogs don't even spawn
 // a second thread, and their methods call (Arm() and Disarm()) return very
 // quickly.
 
 #ifndef BASE_THREADING_WATCHDOG_H_
 #define BASE_THREADING_WATCHDOG_H_
-#pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/platform_thread.h"
 #include "base/time.h"
 
@@ skipping 55 matching lines @@
   ThreadDelegate delegate_;  // Store it, because it must outlive the thread.
 
   TimeTicks start_time_;  // Start of epoch, and alarm after duration_.
 
   DISALLOW_COPY_AND_ASSIGN(Watchdog);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_WATCHDOG_H_