test IWYU fixups for base

base/timer/timer.cc

 // 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.
 
 #include "base/timer/timer.h"
 
+#include <stddef.h>
+
 #include "base/logging.h"
+#include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/threading/platform_thread.h"
 
 namespace base {
 
 // BaseTimerTaskInternal is a simple delegate for scheduling a callback to
 // Timer in the thread's default task runner. It also handles the following
 // edge cases:
 // - deleted by the task runner.
@@ skipping 159 matching lines @@
     PostNewScheduledTask(delay_);
   else
     Stop();
 
   task.Run();
 
   // No more member accesses here: *this could be deleted at this point.
 }
 
 }  // namespace base