Sync the generic vertex attribute data. BUG=angleproject:883 Change-Id: If5616bf24c1ac5477ae80cf1d25efa70b62edea1 Reviewed-on: https://chromium-review.googlesource.com/268750 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Brandon Jones <bajones@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>