Cache TTypes. This change saves us ~70KiB per compiler with just ~3KiB of cache. BUG=492725 Change-Id: I2ee748f7271b1afe0834083cbff6f0b84104aa53 Reviewed-on: https://chromium-review.googlesource.com/281411 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Dmitry Skiba <dskiba@google.com>