This makes the naming more consistent with the rest of the EGL
extensions.

BUG=angleproject:2086

Change-Id: If08e7a550d6b99fb5a3a2138b0c94afc82b2b417
Reviewed-on: https://chromium-review.googlesource.com/578368Reviewed-by: Geoff Lang <geofflang@chromium.org>