Use get_or_create_merge_base in git-cl-upload to correctly deal with rebased

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 17 matching lines @@
 except ImportError:
   pass
 
 
 from third_party import colorama
 from third_party import upload
 import breakpad  # pylint: disable=W0611
 import clang_format
 import fix_encoding
 import gclient_utils
+import git_common
+import owners_finder
 import presubmit_support
 import rietveld
 import scm
 import subcommand
 import subprocess2
 import watchlists
-import owners_finder
 
 __version__ = '1.0'
 
 DEFAULT_SERVER = 'https://codereview.appspot.com'
 POSTUPSTREAM_HOOK_PATTERN = '.git/hooks/post-cl-%s'
 DESCRIPTION_BACKUP_FILE = '~/.git_cl_description_backup'
 GIT_INSTRUCTIONS_URL = 'http://code.google.com/p/chromium/wiki/UsingGit'
 CHANGE_ID = 'Change-Id:'
 
 # Valid extensions for files we want to lint.
@@ skipping 489 matching lines @@
           else:
             DieWithError("""Unable to determine default branch to diff against.
 Either pass complete "git diff"-style arguments, like
   git cl upload origin/master
 or verify this branch is set up to track another (via the --track argument to
 "git checkout -b ...").""")
 
     return remote, upstream_branch
 
   def GetCommonAncestorWithUpstream(self):
-    return RunGit(['merge-base', self.GetUpstreamBranch(), 'HEAD']).strip()
+    return git_common.get_or_create_merge_base(self.GetBranch(),
+                                               self.GetUpstreamBranch())
 
   def GetUpstreamBranch(self):
     if self.upstream_branch is None:
       remote, upstream_branch = self.FetchUpstreamTuple(self.GetBranch())
       if remote is not '.':
         upstream_branch = upstream_branch.replace('heads', 'remotes/' + remote)
       self.upstream_branch = upstream_branch
     return self.upstream_branch
 
   def GetRemoteBranch(self):
@@ skipping 1583 matching lines @@
   group.add_option(
       "-b", "--bot", action="append",
       help=("IMPORTANT: specify ONE builder per --bot flag. Use it multiple "
             "times to specify multiple builders. ex: "
             "'-bwin_rel:ui_tests,webkit_unit_tests -bwin_layout'. See "
             "the try server waterfall for the builders name and the tests "
             "available. Can also be used to specify gtest_filter, e.g. "
             "-bwin_rel:base_unittests:ValuesTest.*Value"))
   group.add_option(
       "-m", "--master", default='',
-      help=("Specify a try master where to run the tries."))           
+      help=("Specify a try master where to run the tries."))
   group.add_option(
       "-r", "--revision",
       help="Revision to use for the try job; default: the "
            "revision will be determined by the try server; see "
            "its waterfall for more info")
   group.add_option(
       "-c", "--clobber", action="store_true", default=False,
       help="Force a clobber before building; e.g. don't do an "
            "incremental build")
   group.add_option(
@@ skipping 371 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:]))