Bug 1062100 - Part 1: Remove ItemCoversScrollableArea. r=mattwoodrow, a=lmandel

This isn't really part of this bug but it simplifies related code.
Bug 1062100 - Part 2: Assign clip rects to non-async-scrollable scrolled layers, and hide clipped layers if some non-moving layer covers their entire clip rect. r=mattwoodrow, a=lmandel
Bug 1062100 - Part 3: When layers are flattened, let all the layers contribute opaqueness to the container layer, whatever their animated geometry roots are. r=tn, a=lmandel
Bug 1059674 - Use AsynchShutdown.blocker() for AddonManager provider shutdown. r=unfocused, r=yoric, a=lmandel
Bug 1074135 - Callback after exceptions when calling async provider methods. r=unfocused, a=lmandel
Bug 1072740 - Translation - Implement doorhanger for in-product promotion. r=felipe, a=lmandel
Bug 1072742 - Add more language targets for translation. r=felipe, a=lmandel
Bug 1072743 - Land Es/Vi/Tr/Pl strings for the promotional translation doorhanger. r=felipe, a=lmandel
Bug 1078163 - WorkerNavigator strings should honor general.*.override prefs in e10s mode. r=khuey, a=lmandel