git_cl: Enable updating description from local.

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index a1f58c8561f8129afd9cab9cf3de775fd5864d87..b8f688cfbfb23c17c7340608daa95a037b21663d 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -3580,7 +3580,8 @@ def CMDdescription(parser, args):
   parser.add_option('-d', '--display', action='store_true',
                     help='Display the description instead of opening an editor')
   parser.add_option('-n', '--new-description',
-                    help='New description to set for this issue (- for stdin)')
+                    help='New description to set for this issue (- for stdin, '
+                         '+ to load from local commit HEAD)')
 
   _add_codereview_select_options(parser)
   auth.add_auth_options(parser)
@@ -3619,6 +3620,10 @@ def CMDdescription(parser, args):
     text = options.new_description
     if text == '-':
       text = '\n'.join(l.rstrip() for l in sys.stdin)
+    elif text == '+':
+      base_branch = cl.GetCommonAncestorWithUpstream()
+      merge_base = RunGit(['merge-base', base_branch, 'HEAD']).strip()
+      text = CreateDescriptionFromLog([merge_base])

[agable, 2016/09/02 16:43:00]

This produces a commit message which is not of the standard
"""
Single short line

Paragraph of more descriptive text which may
take up more than one line, but is separated
from the first line by a single blank line.
"""
format.

[dnj, 2016/09/02 17:31:40]

I don't think this is correct. When I run the command, I get the same commit
message that is in the log, which is what I want this to do. I hacked this CL to
print the "text" return value, and I get:

$ git cl description -n +

git_cl: Enable updating description from local.

Currently, if one edits one's local CL description (e.g., `git commit
--amend`), there is no path for that update to get pushed to Rietveld.
This adds a "+" sentinel to the "-n" flag for `git cl description` that
tells it to load description content from the local commit.

BUG=None
TEST=local

[agable, 2016/09/02 17:43:39]

Ah. We develop differently. I often have 2-10 commits on a branch, and none of
them have a full commit description like gets uploaded to review. That only
comes into existence when I do git-cl-upload. For me, this produces a
conglomeration of all those one-line commit messages, one after the other. This
is really only useful if you only have a single commit on the branch.

Maybe this should only upload the latest commit message, as opposed to the log
back to the merge-base?

[dnj, 2016/09/02 18:05:55]

I revised this to do the same thing "git cl upload" does, so this should now be
consistent with that expectation.

 
     description.set_description(text)
   else: