Rename ZoneTypeCache to TypeCache and use a single shared (immutable)
instance consistently to cache the most commonly used types. Also serves
as a chokepoint for defining those types, so we don't repeat the
definition (and possible bugs) in various places.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1409763004

Cr-Commit-Position: refs/heads/master@{#31631}