Also refactor some query extension entry points.

BUG=angleproject:747

Change-Id: I5a8a3b2616a3872b5645a655641ec9c12739f804
Reviewed-on: https://chromium-review.googlesource.com/636062Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>