This is simply done by specifying max_vertices=1.

Bug: angleproject:5411
Change-Id: I50318128cca0e96a8b7c7e5d01165b9ef46b4db8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2574823
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>