This is a preparation for more dirty bits. It moves the driver
constant buffer application into the state manager, redesigns
how the dirtiness is tracked (no more memcmp) and also removes
a couple of virtual calls.

BUG=angleproject:1390
BUG=angleproject:2052

Change-Id: I41a75c280600ad8ba1f23c721d436214a116422a
Reviewed-on: https://chromium-review.googlesource.com/659223
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>