Code review comment for lp:~afrantzis/mir/client-api-platform-operation-fds

LGTM,

comment on a pre-existing issue, but
185 + repeated sint32 fd = 3;

Forces us to strip the ownership info of the FD's at a point before the ipc-processing code is dispatched with the message. I guess this is the price to pay for having SessionMediator inherit from the protobuf-generated stub, but it would be nice to have mir:Fd make it to the ipc-code and not have to deal with resource caches.