Defer testing composition to a later time (A70)

This is not exactly the same logically speaking, because it's
theoretically possible that the composing state changed in between
the message enqueueing and it's retrieval. However in the practice,
if the composing state changed the message *must* have been
cancelled and resent, else the behavior breaks. So this actually
is more robust, and removes some obscure requirements on the
calling code.

In the practice, it should also make the cancelUpdateSuggestionStrip
message useless, although this change does not yet remove it.

Change-Id: I75141920ce64e38e2f92e9c02b6c979936eee9a9