Implement drawRangeElements in RendererGL. BUG=angleproject:1136 Change-Id: I8b84b845da09f60bfd5e8f400da47d759f0d8f1a Reviewed-on: https://chromium-review.googlesource.com/295234 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>