A page host dispatches its events synchronously, so it can answer (a
saved for the save the handler just posted) while the handler is still
running. The nested borrow_mut then panicked. Both transports now hand
messages to an Inbox that queues each one and drains the queue one call
at a time, in order; nothing is dropped. The new test fails with the old
borrow ("already borrowed").
FileData::size() reads a Blob's length from the Blob; a host's size
field is no longer trusted for an app's size check. lib.rs gets the
crate-level deny of unwrap, expect, panic and the like.
Helen Kwok
ae1fa48449