Previously, git cl upload would send email every time.
This CL changes that to send email only if -s or --send-mail is given.

R=andybons@chromium.org
BUG=612728

Review-Url: https://codereview.chromium.org/2007873002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300662 0039d316-1c4b-4281-b951-d872f2087c98