This works in that it actually changes the description, but after
multiple changes, there's multiple footers added. I'm not sure if they
should be stripped in setting the description? Or is the problem in
FetchDescription() where it shouldn't be returning
'commit_with_footers', but rather something else?

Example change at https://chromium-review.googlesource.com/c/340430/.

R=tandrii@chromium.org
BUG=603207

Review URL: https://codereview.chromium.org/1917473002 .

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300169 0039d316-1c4b-4281-b951-d872f2087c98