Enable event regions.
Stash hacks to repro test failure
Bug 1109263 - Clamp the reftest drawWindow call to the canvas. r=

In some cases the area reported by MozAfterPaint can be extremely large. Since
that area determines what we pass to drawWindow, we could end up trying to
drawWindow an area that is too large for drawWindow to handle. Instead, this
patch clamps that area to the canvas size so that we don't unnecessarily try to
paint (and fail at painting) the whole invalid area.
Bug 1107404 - Ensure that display items don't fall through an event regions item into a different layer. r=
Bug 1098654 - Improve layerization of display items when dealing with async scrollable layers. r=

The function IsSubjectToAsyncTransforms() was not correctly reporting when a
layer was actually subject to async transforms. As a result, sometimes display
items from above such a layer would end up in a layer below. This could
manifest as page elements being improperly covered by async scrolling elements.