Add an extension to share textures at the display level. BUG=angleproject:1639 Change-Id: If9140142ebce89f33921c13d9d212c17d1894162 Reviewed-on: https://chromium-review.googlesource.com/437618 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>