In retrospect, overloading `Connection::connectionReady` to mean
"is ready _and_ supports this operation" wasn't a good idea. This
commit reverts that change (cfd44c936a9b), and adds two new methods:
* `Connection::operationSupported`, to check if a connection supports
sync or async operations. This method is public.
* `Connection::ensureOperationSupported`, that asserts or returns an
error if the connection doesn't support an operation. This is
private.
`operationSupported` is used by callers like `Service::minimizeMemory`
to detect if the connection supports sync operations, since both sync
and async connections implement `mozIStorageConnection` now.
Finally, some callers used `!mDBConn` to check if the connection was
ready, while others used `connectionReady()`. This commit changes them
to use the latter.
Differential Revision: https://phabricator.services.mozilla.com/D24974
--HG--
extra : moz-landing-system : lando
0cdebe20d7