In preparation for support of primitives generated queries.

Bug: angleproject:5404
Change-Id: Ic123aaff33f8903994ff8fcc9158954ac023ec13
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2562126
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Charlie Lao <cclao@google.com>