In the next CL, the Context is going to remove the mutable getter
for the gl::State. This means we can only mutate the state inside
Context. So, we need to move all the state mutating GL command
implementations to gl::Context.
BUG=angleproject:747
BUG=angleproject:1388
Change-Id: I9ed351d08611934bf708781c6af3948396921593
Reviewed-on: https://chromium-review.googlesource.com/351171Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
