nsQueryReferent is defined as an nsCOMPtr_helper, which implies that
calling its operator() method requires a virtual call. While
nsQueryReferent is marked `final`, compiler inlining decisions make it
impossible to de-virtualize the call to operator(). However, we have
many other classes returned by do_* functions that nsCOMPtr handles
directly, requiring no extra virtual calls, and we can give
nsQueryReferent the same treatment.
