Surface: query swapBehavior from the Impl All the previously implemented surfaces used to preserve the content of the surface on a swap but this is no longer the case with CGL. BUG=angleproject:891 Change-Id: I264c579bcbbd22b4eeb09e78aa95751d223694fc Reviewed-on: https://chromium-review.googlesource.com/289871 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>