simplify a few header includes

base/tracked_objects.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/tracked_objects.h"
 
 #include <math.h>
+#include <stdlib.h>
 
 #include "base/format_macros.h"
-#include "base/message_loop.h"
 #include "base/profiler/alternate_timer.h"
 #include "base/stringprintf.h"
 #include "base/third_party/valgrind/memcheck.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "base/port.h"
 
 using base::TimeDelta;
 
 namespace tracked_objects {
@@ skipping 861 matching lines @@
        ++it) {
     base::DictionaryValue* parent_child = new base::DictionaryValue;
     it->first->ToValue("parent", parent_child);
     it->second->ToValue("child", parent_child);
     descendants->Append(parent_child);
   }
   dictionary->Set("descendants", descendants);
 }
 
 }  // namespace tracked_objects