Move display extension initialization to DisplayImpl. BUG=angle:658 Change-Id: I44d95fad4e1be5cc76f443d724defd37da4a268f Reviewed-on: https://chromium-review.googlesource.com/234762 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Brandon Jones <bajones@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>