Apply Issue shim for disabling checkout when bot update ran.

checkout.py

 # coding=utf8
 # 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.
 """Manages a project checkout.
 
 Includes support for svn, git-svn and git.
 """
 
 import ConfigParser
@@ skipping 535 matching lines @@
           ['log', '-q', self.svn_url, '-r', '%s:%s' % (rev1, rev2)])
     except subprocess.CalledProcessError:
       return None
     # Ignore the '----' lines.
     return len([l for l in out.splitlines() if l.startswith('r')]) - 1
 
 
 class GitCheckout(CheckoutBase):
   """Manages a git checkout."""
   def __init__(self, root_dir, project_name, remote_branch, git_url,
-      commit_user, post_processors=None):
+      commit_user, post_processors=None, base_ref=None):
     super(GitCheckout, self).__init__(root_dir, project_name, post_processors)
+    self.base_ref = base_ref
     self.git_url = git_url
     self.commit_user = commit_user
     self.remote_branch = remote_branch
     # The working branch where patches will be applied. It will track the
     # remote branch.
     self.working_branch = 'working_branch'
     # There is no reason to not hardcode origin.
     self.remote = 'origin'
     # There is no reason to not hardcode master.
     self.master_branch = 'master'
@@ skipping 135 matching lines @@
             'While running %s;\n%s%s' % (
               ' '.join(e.cmd),
               align_stdout(stdout),
               align_stdout([getattr(e, 'stdout', '')])))
     # Once all the patches are processed and added to the index, commit the
     # index.
     cmd = ['commit', '-m', 'Committed patch']
     if verbose:
       cmd.append('--verbose')
     self._check_call_git(cmd)
+    if self.base_ref:
+      base_ref = self.base_ref
+    else:
+      base_ref = '%s/%s' % (self.remote,
+                            self.remote_branch or self.master_branch)
     found_files = self._check_output_git(
-        ['diff', '%s/%s' % (self.remote,
-                            self.remote_branch or self.master_branch),
+        ['diff', base_ref,
          '--name-only']).splitlines(False)
     assert sorted(patches.filenames) == sorted(found_files), (
         sorted(patches.filenames), sorted(found_files))
 
   def commit(self, commit_message, user):
     """Commits, updates the commit message and pushes."""
     assert self.commit_user
     assert isinstance(commit_message, unicode)
     current_branch = self._check_output_git(
         ['rev-parse', '--abbrev-ref', 'HEAD']).strip()
@@ skipping 99 matching lines @@
   def revisions(self, rev1, rev2):
     return self.checkout.revisions(rev1, rev2)
 
   @property
   def project_name(self):
     return self.checkout.project_name
 
   @property
   def project_path(self):
     return self.checkout.project_path