[DL]: Add promise rejection reasons.

This patch adds reasons for rejection for each promise that is rejected.

R=chrishtr@chromium.org

Bug: 882663
Change-Id: I3317862ca5bf8cd76ad7309d61f7ec38e76c9e4d
Reviewed-on: https://chromium-review.googlesource.com/c/1452493
Commit-Queue: vmpstr <vmpstr@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629265}
35 files changed