Bug 939607 - Part 1: Make PaintBoxShadowOuter take an opacity value. r=roc
Bug 939607 - Part 2: Add an API for storing an opacity on a display item, and implement it for nsDisplayBoxShadowOuter. r=roc
Bug 939607 - Part 3: Try fold nsDisplayOpacity items opacity value into their children. r=roc
Bug 939607 - Part 4: Add test for box-shadow with opacity. r=roc