Save the CL locally prior to attempting to submit
to Rietveld.  The CL is saved locally with a dirty-bit
before the upload is attempted.  If successful, the CL
is saved locally again with a clean-bit.

On loading a dirty CL for editing, we only load the
CL description from Rietveld if the local CL is clean
(there are no pending changes to upload).  Clean CLs
continue to retrieve updated descriptions directly
from Rietveld.

BUG=none
TEST=gcl change <name> saves CL description local
prior to uploading.  gcl change <name> after a failed
Rietveld upload uses local CL description instead of
using the associated issue's description from Rietveld.
Changes in this state are reset to the 'clean' state
after the Rietveld update completes.
Review URL: http://codereview.chromium.org/428001

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@32791 0039d316-1c4b-4281-b951-d872f2087c98