nsRefreshDriver::ObserverArray is a nsTObserverArray which is
infallible, so no need to check the return value from AppendElement
(which a later patch in this series will remove).
We implement PointerEvent.getCoalescedEvents as
1. Clone the widget events we coalesced.
2. Convert them to dom::PointerEvent when user calls getCoalescedEvents.
MozReview-Commit-ID: 8IKw4PbUsDD
Sylvestre Ledru
Mats Palmgren
Stone Shih