nsIEventListenerChange::changedListenerNames is an nsIArray attribute that
contains nsIAtoms. Bug 1396693 made it `noscript` to help with nsIAtom
deCOMtamination (bug 1392883) but more changes are needed: that array
eventually needs to be changed to nsTArray<RefPtr<nsIAtom>>.
Turns out the attribute has a single use, in a11y code. That code merely
iterates over the list and counts how many atoms it contains that match
"onclick", "onmousedown", and "onmouseup".
So this patch moves that counting functionality inside nsEventListenerChange by
changing the attribute to `countOfEventListenerChangesAffectingAccessibility`.
This saves us from having to expose the array of atoms via XPIDL.
--HG--
extra : rebase_source : db8b628998d45209ab724555a74efe90f431d3ae
49963dad55