Use invalidation sets for some pseudo elements.

Allow to use class invalidation sets for selectors containing ::before,
::after, or ::backdrop. These pseudo elements are updated correctly in
Element::recalcChildStyle for LocalStyleChange on their parents.

BUG=335247

Review URL: https://codereview.chromium.org/195093004

git-svn-id: svn://svn.chromium.org/blink/trunk@169298 bbb929c8-8fbe-4397-9dbb-9b2b20218538