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

url/ipc/url_param_traits.h

Index: url/ipc/url_param_traits.h
diff --git a/url/ipc/url_param_traits.h b/url/ipc/url_param_traits.h
index f40150f110d65f4fe6806c65e920c070a51ea8bb..8db4029484615778bde2ea9bcf22812700b01f6e 100644
--- a/url/ipc/url_param_traits.h
+++ b/url/ipc/url_param_traits.h
@@ -14,6 +14,7 @@ namespace IPC {
 template <>
 struct URL_IPC_EXPORT ParamTraits<GURL> {
   typedef GURL 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,