Remove usesBeforeAfterRules RuleFeatureSet flag

Almost every real world complex page uses ::before or ::after from my sampling
and all this flag does is let us skip a few if statements inside recalcStyle
and the loop inside RenderStyle::getCachedPseudoStyle which is suspect since
we always go through an essentially identical loop in
Element::pseudoStyleCacheIsInvalid (and since most elements have no pseudos).

We should just remove this "fast path" code.

Review URL: https://chromiumcodereview.appspot.com/23479006

git-svn-id: svn://svn.chromium.org/blink/trunk@156798 bbb929c8-8fbe-4397-9dbb-9b2b20218538