Add cq_build_durations for CQ-master builds.

Add cq_build_durations for CQ-master builds to reflect distribution
metrics for self-destructed CQs and not-self-destructed CQs.

BUG=chromium:677178
TEST=unit_tests

Change-Id: I60bd07b5d9a0b5342569981586793d6d8d7f4e4c
Reviewed-on: https://chromium-review.googlesource.com/457787
Commit-Ready: Ningning Xia <nxia@chromium.org>
Tested-by: Ningning Xia <nxia@chromium.org>
Reviewed-by: Paul Hobbs <phobbs@google.com>
3 files changed