Refactor BeginQuery validation out of gl::Context. Part of our effort to relocate all validation logic to a preliminary pass outside of our state tracking or rendering layers. BUG=angle:571 Change-Id: I5241daef6249910a781e78fd066debe0ab1d3f2b Reviewed-on: https://chromium-review.googlesource.com/199348 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>