Bug 1106651 - [Keyboard] When using edge gesture while a keyboard is shown, black appears in place of keyboard space and app freezes 

https://bugzilla.mozilla.org/show_bug.cgi?id=1106651
Implement activeApp.isSheetTransitioning() which returns this.element.classList.contains('inside-edges') please.
It makes no sense to couple NfcManager and SheetTransition together.