getSwapBehavior was being called in Surface's constructor but masn't
expected, causing a warning. Add it as an expect call.

BUG=angleproject:1126

Change-Id: Idf4a7e0ff66ba5741d3773e09ade4a1335b355ae
Reviewed-on: https://chromium-review.googlesource.com/293902Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>