Move validation of EndQuery out of gl::Context.

BUG=angle:571

Change-Id: I8913eb1b565a4282d9d84d06933e8b854453f17d
Reviewed-on: https://chromium-review.googlesource.com/199349
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
12 files changed