Adds functionality to presubmit api to return error,
notification and warning messages caught in
presubmit_support.py in the form of a json.

Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: build_limited_scripts_slave
Bug:971895
Change-Id: I42a3df3994077342216d002381b6135012b4334c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1666250
Commit-Queue: Debrian Figueroa <debrian@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>