This is the ANGLE side of a two-sided patch including Chromium to
rename this synthetic OpenGL extension to use an ANGLE_ prefix.

Bug: chromium:1011653
Change-Id: Ice4b526a34157ebbd8c283aacc9437fae2e35d6e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1843506Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>