Revision (or more accurately, its upcoming MCR replacement) should allow
for the full flexibility of CommentStore in its interface, and the most
straightforward way to do that is to use CommentStoreComment. But for
that to work sanely, we need a non-@private way to create a new
CommentStoreComment that hasn't been saved to the database yet.
Change-Id: I76028e8ef3da4568a16e098cdfbc806a67b814e3
Since the caller doesn't (and shouldn't) know whether CommentStore is
using the old or the new schema, it should leave truncation of comments
to CommentStore.
Change-Id: I92954c922514271d774518d6a6c28a01f33c88c2
