CSS selector matching optimizations

Today:

• Naive linear scan through rules.

Optimizations we need:

• ID hash, class hash, tag hash (issue #1167).
• Parallel matching (landed but needs tuning).
  – In Zoomm paper, need parallel top down traversal.
  – Need to be careful about overhead of distributing work.
• Interning.
• “What’s above me?” Bloom filter—see Zoomm work.