Generate param traits size methods for IPC files in content/ (and traits it depends on).

ui/events/ipc/latency_info_param_traits.h

Index: ui/events/ipc/latency_info_param_traits.h
diff --git a/ui/events/ipc/latency_info_param_traits.h b/ui/events/ipc/latency_info_param_traits.h
index 9e11104341fc6d3907db26c35542555304011673..0083e6dae2d92765ad21c26379f88ad5f08f03a7 100644
--- a/ui/events/ipc/latency_info_param_traits.h
+++ b/ui/events/ipc/latency_info_param_traits.h
@@ -12,6 +12,7 @@ namespace IPC {
 template <>
 struct EVENTS_IPC_EXPORT ParamTraits<ui::LatencyInfo> {
   typedef ui::LatencyInfo param_type;
+  static void GetSize(base::PickleSizer* s, const param_type& p);
   static void Write(base::Pickle* m, const param_type& p);
   static bool Read(const base::Pickle* m,
                    base::PickleIterator* iter,