Code review comment for lp://staging/~vanvugt/mir/schedule-nonblocking

I remember there's something in this area that doesn't work as I expect: This codepath ought to be a corner case that occurs rarely, if ever. But it happens a lot.

We shouldn't be doing IPC on the composite thread at all: re-ordering the operations is just moving the deckchairs.

I haven't tried, but I don't see why this is easier than queuing the IPC to happen on the "Mir/IPC" thread.