nsStyleContext::CalcDifference had an optimization where, when we knew
that the old and new style context have the same rule node, we knew that
the only change hints that would need to be handled are those in the
"not handled for descendants" category, generated due to explicit
'inherit' values on reset properties. This was because any changes due
to differences in inherited properties should only have generated
"handled for descendants" change hints (and thus would already have been
handled on an ancestor).
Before bug 931668, this let us avoid calling CalcDifference on structs
that only would have generated hints that we knew we already would have
handled. However, after bug 931668, we compare all structs anyway so
that we can set the aEqualStructs outparam, so we don't gain anything
from this optimization. We can still return these change hints we know
will not need to be handled, and rely on ElementRestyler::CaptureChange
to filter them out.
MozReview-Commit-ID: Ld1s2Js0i6r
cf56de72b5