This CL introduces a coarse layer of dirty bits and on-demand sending of
some uniforms to the underlying driver, instead of sending all uniforms
every draw, which should improve performance in cases where not much is
changing between draws.

BUG=angleproject:2306

Change-Id: I530515dfad2e4be74c73d8659acd4fe5decaa8b0
Reviewed-on: https://chromium-review.googlesource.com/c/1361222Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Lingfeng Yang <lfy@google.com>