Add a family of git-commands to assist with the management of multiple CLs/branches.

git-rebase-update - ensure all branches are up to date
git-new-branch - create branches
git-rename-branch - rename a branch while preserving parentage relationships
git-reparent-branch - change the parent of a branch, including rebasing it correctly onto that new parent.
git-squash-branch - collapse a branch into a single commit
git-upstream-diff - show the diff between the current branch and it's upstream branch
git-mark-merge-base - explicitly set what you want the above tools to consider the merge-base for the current branch.

R=agable@chromium.org, hinoka@chromium.org, stip@chromium.org, szager@chromium.org
BUG=261738

Review URL: https://codereview.chromium.org/184253003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@259520 0039d316-1c4b-4281-b951-d872f2087c98

git_new_branch.py

@@ -0,0 +1,53 @@
+#!/usr/local/bin/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.
+
+import argparse
+import sys
+
+import subprocess2
+
+from git_common import run, root, set_config, get_or_create_merge_base, tags
+from git_common import hash_one
+
+
+def main(args):
+  parser = argparse.ArgumentParser(
+    formatter_class=argparse.ArgumentDefaultsHelpFormatter
+  )
+  parser.add_argument('branch_name')
+  g = parser.add_mutually_exclusive_group()
+  g.add_argument('--upstream_current', action='store_true',
+                 help='set upstream branch to current branch.')
+  g.add_argument('--upstream', metavar='REF', default=root(),
+                 help='upstream branch (or tag) to track.')
+  g.add_argument('--lkgr', action='store_const', const='lkgr', dest='upstream',
+                 help='set basis ref for new branch to lkgr.')
+
+  opts = parser.parse_args(args)
+
+  try:
+    if opts.upstream_current:
+      run('checkout', '--track', '-b', opts.branch_name)
+    else:
+      if opts.upstream in tags():
+        # TODO(iannucci): ensure that basis_ref is an ancestor of HEAD?
+        run('checkout', '--no-track', '-b', opts.branch_name,
+            hash_one(opts.upstream))
+        set_config('branch.%s.remote' % opts.branch_name, '.')
+        set_config('branch.%s.merge' % opts.branch_name, opts.upstream)
+      else:
+        # TODO(iannucci): Detect unclean workdir then stash+pop if we need to
+        # teleport to a conflicting portion of history?
+        run('checkout', '--track', opts.upstream, '-b', opts.branch_name)
+
+    get_or_create_merge_base(opts.branch_name)
+  except subprocess2.CalledProcessError as cpe:
+    sys.stdout.write(cpe.stdout)
+    sys.stderr.write(cpe.stderr)
+    return 1
+
+
+if __name__ == '__main__':  # pragma: no cover
+  sys.exit(main(sys.argv[1:]))