Support tag names as invalidation set features.

We collected the tag names into the invalidation sets, but we never used them
for anything. This makes selectors like this use invalidation sets:

.class span {}

R=esprehn@chromium.org,chrishtr@chromium.org
BUG=335247

Review URL: https://codereview.chromium.org/222643002

git-svn-id: svn://svn.chromium.org/blink/trunk@170807 bbb929c8-8fbe-4397-9dbb-9b2b20218538