Bug 858937 patch 1: Add nsLayoutUtils::GetStyleFrame() variant taking nsIContent*, and use it for two existing users of the variant taking nsIFrame*.  r=nrc
Bug 858937 patch 2:  Make off-main-thread CSS transitions/animations code that should be using nsLayoutUtils::GetStyleFrame do so.  r=nrc

The fixes to the miniflush code
(nsTransitionManager::UpdateThrottledStyle and UpdateAllThrottledStyles)
fix the case where we constructed totally incorrect style contexts for
outer table frames (which have special style contexts inheriting from
the table frame) during the miniflush, leading to inconsistent style
data and other bad things, when we should have been touching the style
on the table frame instead.

The fixes to the other OMTA codepaths lead to layer tests being
performed on the same frame that the styles will be applied to, and
probably fix real bugs (which would occur when animating opacity or
transform on a table).