Make git_map properly update merge base markers.

git_map.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """
 Provides an augmented `git log --graph` view. In particular, it also annotates
 commits with branches + tags that point to them. Items are colorized as follows:
   * Cyan    - Currently checked out branch
   * Green   - Local branch
   * Red     - Remote branches
   * Magenta - Tags
   * White   - Merge Base Markers
   * Blue background - The currently checked out commit
 """
 
 import sys
 
 import subprocess2
 
 from git_common import current_branch, branches, tags, config_list, GIT_EXE
-from git_common import branch_config_map, root
+from git_common import get_or_create_merge_base, root
 
 from third_party import colorama
 
 CYAN = colorama.Fore.CYAN
 GREEN = colorama.Fore.GREEN
 MAGENTA = colorama.Fore.MAGENTA
 RED = colorama.Fore.RED
 WHITE = colorama.Fore.WHITE
 
 BLUEBAK = colorama.Back.BLUE
 
 BRIGHT = colorama.Style.BRIGHT
 RESET = colorama.Fore.RESET + colorama.Back.RESET + colorama.Style.RESET_ALL
 
 # Git emits combined color
 BRIGHT_RED = '\x1b[1;31m'
 
 def main():
   map_extra = config_list('depot_tools.map_extra')
   fmt = '%C(red bold)%h%x09%Creset%C(green)%d%Creset %C(yellow)%ad%Creset ~ %s'
   log_proc = subprocess2.Popen(
     [GIT_EXE, 'log', '--graph', '--branches', '--tags', root(),
      '--color=always', '--date=short', ('--pretty=format:' + fmt)
     ] + map_extra + sys.argv[1:],
     stdout=subprocess2.PIPE,
     shell=False)
 
-  merge_base_map = branch_config_map('base')
   current = current_branch()
   all_branches = set(branches())
+  merge_base_map = {b: get_or_create_merge_base(b) for b in all_branches}
   if current in all_branches:
     all_branches.remove(current)
   all_tags = set(tags())
   try:
     for line in log_proc.stdout.xreadlines():
       if merge_base_map:
         commit = line[line.find(BRIGHT_RED)+len(BRIGHT_RED):line.find('\t')]
         base_for_branches = set()
         for branch, sha in merge_base_map.iteritems():
           if sha.startswith(commit):
@@ skipping 41 matching lines @@
     pass
   finally:
     sys.stderr.close()
     sys.stdout.close()
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())