Treat "Bug:" as an empty line in git cl upload
Treat "Bug:" as an empty line in git cl upload

The default description in the editor when you invoke "git cl upload"
includes recent commit descriptions, some blank lines and comments, and
"Bug: ". The upload script properly strips out the comments but was
leaving in the "Bug:" line. This leads to CLs with blank Bug: lines,
which is sloppy. It also means that if a user changes their mind and
closes the upload editor without adding any content... they would still
have a CL created.

This change removes the "Bug: " line if nothing has been added to it,
thus avoiding uploading a change with an empty description, and avoiding
having meaningless Bug: lines.

Change-Id: I18c2094e5712d31729899c0ebd0a52de97dc4e7f
Reviewed-on: https://chromium-review.googlesource.com/861920
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Bruce Dawson <fe9e26f3989304bf7275ed139c57fd059c63d22d@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools