It also removes the need of manually creating a subject argument.

Other related changes in this CL:
- Reenable the prompt for patchset title in gcl. I'm not sure why it was disabled.
- Remove git cl upload --desc_from_logs flag. --force is already meaningful.

R=cmp@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/9193023

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@119066 0039d316-1c4b-4281-b951-d872f2087c98