cros: re-center oobe ui dialog when keyboard visibility changed

Bug: 841074
Change-Id: I1862d72f637a8044b1051aeac22a4f72c6872036
Reviewed-on: https://chromium-review.googlesource.com/1150635
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Xiaoyin Hu <xiaoyinh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578091}
2 files changed