We were missing the implementation for the instanced draw for these.
Implement them in the same way as for triangle fan.

BUG=angleproject:1101

Change-Id: I444f3a23383c63b8df6f9ebe25b255c8890632a1
Reviewed-on: https://chromium-review.googlesource.com/313007
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>