Send CL notifications from pre-cq-launcher

We will soon be launching multiple pre-cq configs for a CL to improve
the test coverage and performance. To reduce the gerrit comment/email
spam, This CL does the following:

  * Individual pre-cq config no loger comments on the CL after
    applying the changes. Instead, pre-cq-launcher will update the CL
    with URLs to the build statuses after all configs are inflight.

  * Individual pre-cq config no loger comments on the CL after
    successfully verifies the change. Instead, pre-cq-launcher will
    update the CL when marking the CL as passed.

Note that when the pre-cq configs fail, they will still comment on the
CL individually. This issue should be addressed later.

This CL also moves ConstructDashboardURL from validation_pool to
tree_status and uses the waterfall information recorded in the
metadata to construct the URL, as opposed to using the overlays and
the trybot flag. This provides a more accurate information because
overlays are not sufficient to distinguish between ToT, branch, and
release builds.

BUG=chromium:439595
TEST=remote pre-cq-launcher and pre-cq configs

Change-Id: I99da0f99c1f1da15d66039979ddd3cd600bcc9ae
Reviewed-on: https://chromium-review.googlesource.com/234044
Tested-by: Yu-Ju Hong <yjhong@chromium.org>
Trybot-Ready: Yu-Ju Hong <yjhong@chromium.org>
Reviewed-by: Yu-Ju Hong <yjhong@chromium.org>
Commit-Queue: Yu-Ju Hong <yjhong@chromium.org>

0 files changed, 0 insertions, 0 deletions