Stub in more IPC attachment brokering functionality.

ipc/ipc_message_utils.h

Index: ipc/ipc_message_utils.h
diff --git a/ipc/ipc_message_utils.h b/ipc/ipc_message_utils.h
index 96bb6895abb3f08c25dca3af78c7f8a26619ce38..dbbd642ca53c809ad650f567bd33ebb52e95e672 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -20,6 +20,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/tuple.h"
+#include "ipc/brokerable_attachment.h"
 #include "ipc/ipc_message_start.h"
 #include "ipc/ipc_param_traits.h"
 #include "ipc/ipc_sync_message.h"
@@ -432,6 +433,15 @@ struct ParamTraits<std::pair<A, B> > {
   }
 };
 
+// IPC ParamTraits -------------------------------------------------------------
+template <>
+struct IPC_EXPORT ParamTraits<BrokerableAttachment::AttachmentId> {
+  typedef BrokerableAttachment::AttachmentId param_type;
+  static void Write(Message* m, const param_type& p);
+  static bool Read(const Message* m, base::PickleIterator* iter, param_type* r);
+  static void Log(const param_type& p, std::string* l);
+};
+
 // Base ParamTraits ------------------------------------------------------------
 
 template <>