Added error check that we are on a branch when we try to upload.

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 from distutils.version import LooseVersion
@@ skipping 1848 matching lines @@
     return 1
 
   options.reviewers = cleanup_list(options.reviewers)
   options.cc = cleanup_list(options.cc)
 
   cl = Changelist()
   if args:
     # TODO(ukai): is it ok for gerrit case?
     base_branch = args[0]
   else:
+    if cl.GetBranch() is None:
+      DieWithError('Can\'t upload from detached HEAD state. Get on a branch!')
+
     # Default to diffing against common ancestor of upstream branch
     base_branch = cl.GetCommonAncestorWithUpstream()
     args = [base_branch, 'HEAD']
 
   # Apply watchlists on upload.
   change = cl.GetChange(base_branch, None)
   watchlist = watchlists.Watchlists(change.RepositoryRoot())
   files = [f.LocalPath() for f in change.AffectedFiles()]
   if not options.bypass_watchlists:
     cl.SetWatchers(watchlist.GetWatchersForPaths(files))
@@ skipping 1056 matching lines @@
         ('AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
           'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
 
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   colorama.init()
   sys.exit(main(sys.argv[1:]))