Completion search used for type-ahead should make use of http caches,
like ApiOpenSearch does.
Bug: T245675
Change-Id: Ia8366684203381b6c4dc55669a6877e53e9ffe40
Saw a function comment in Handler.php for needsWriteAccess() that stated: "The handler should override this if the route does not need to write to the database."
Adding that function in SearchHandler.php.
Change-Id: Ib320deb3f3f5464a50e8486142cc106a310948da
