[DL]: Ensure to reject update/commit promises on disconnected elements.

This patch ensures that we reject update/commit when it happens on
a disconnected element.

R=chrishtr@chromium.org

Bug: 882663
Change-Id: Iaee923a4f41714b437c0a2b85bbb175359a2f32c
Reviewed-on: https://chromium-review.googlesource.com/c/1387944
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618713}
6 files changed