posix: cut down on IPC logging spew a bit

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 523ce6032bb38c652bda818ecc6f1d9a7b366c22..4e25b855521eba7ab8ff88c88ebf5d4939c6ac9d 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -753,7 +753,7 @@ struct ParamTraits<XFORM> {
 struct LogData {
   std::string channel;
   int32 routing_id;
-  uint16 type;
+  uint16 type;  // "User-defined" message type, from ipc_message.h.
   std::wstring flags;
   int64 sent;  // Time that the message was sent (i.e. at Send()).
   int64 receive;  // Time before it was dispatched (i.e. before calling