Also accompanying hand edits to validationES2.cpp and
Context.cpp to allow linking.

Bug: angleproject:3188
Change-Id: I89832265092fabc71bade464f0171d65038d8b0e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1648454
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>