This will make explanation provided by Rietveld visible to the user, e.g.
"Request to https://codereview.chromium.org/1386443003/edit_flags failed: Cannot
set commit on an issue that does not have a commit queue".

R=phajdan.jr@chromium.org
BUG=529339

Review URL: https://codereview.chromium.org/1387833002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@297009 0039d316-1c4b-4281-b951-d872f2087c98