iwyu: Cleanup in the following files:

base/at_exit.cc

-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// 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.
 
 #include "base/at_exit.h"
+
+#include <stddef.h>
+#include <ostream>
+
 #include "base/logging.h"
 
 namespace base {
 
 // Keep a stack of registered AtExitManagers.  We always operate on the most
 // recent, and we should never have more than one outside of testing, when we
 // use the shadow version of the constructor.  We don't protect this for
 // thread-safe access, since it will only be modified in testing.
 static AtExitManager* g_top_manager = NULL;
 
@@ skipping 42 matching lines @@
     callback_and_param.func_(callback_and_param.param_);
   }
 }
 
 AtExitManager::AtExitManager(bool shadow) : next_manager_(g_top_manager) {
   DCHECK(shadow || !g_top_manager);
   g_top_manager = this;
 }
 
 }  // namespace base