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

ipc/mach_port_mac.cc

Index: ipc/mach_port_mac.cc
diff --git a/ipc/mach_port_mac.cc b/ipc/mach_port_mac.cc
index 9375d728eab5740899b9a0a72fae098d562eecdd..a482d24d7f03ee1d4de77b773bbf89fe43f00b9a 100644
--- a/ipc/mach_port_mac.cc
+++ b/ipc/mach_port_mac.cc
@@ -12,6 +12,12 @@
 namespace IPC {
 
 // static
+void ParamTraits<MachPortMac>::GetSize(base::PickleSizer* s,
+                                       const param_type& p) {
+  s->AddAttachment();
+}
+
+// static
 void ParamTraits<MachPortMac>::Write(base::Pickle* m, const param_type& p) {
   if (!m->WriteAttachment(
           new IPC::internal::MachPortAttachmentMac(p.get_mach_port()))) {