The GL layer can interact with the translator directly, to query all
the active shader variables and call ShCompile.

BUG=angleproject:1159

Change-Id: I334a9bef28f93cf85dd8cac0fb8542ac567cc3ec
Reviewed-on: https://chromium-review.googlesource.com/299877Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>