gclient: update git-cl whenever git-cl is run and not when gclient is run

git-cl

 #!/bin/sh
 # Copyright (c) 2010 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.
 
 base_dir=$(dirname "$0")
 repo="$base_dir/git-cl-repo"
 url="http://src.chromium.org/git/git-cl.git"
 cur_url=$(git config -f "$repo/.git/config" remote.origin.url)
 
 if [ -e "$repo" -a "$cur_url" != "$url" ]; then
   cat <<EOF
 $repo
 is tracking a non-default remote repository:
 
   default: $url
   yours:   $cur_url
 
 This is intended to be an automatically-updating, read-only repository.
 Please create a separate repository for making changes to git-cl, move your
 modifications there, and then run:
   rm -rf $repo
 EOF
   exit 1
 fi
 
 if [ ! -f "$repo/git-cl" ]; then
   git clone $url $repo -q
+elif [ ! -e "$base_dir/git-cl-repo/.git" ]; then
+  echo "$0: $base_dir/git-cl-repo does not appear to be a git repo"
+elif [ "X$DEPOT_TOOLS_UPDATE" != "X0" ]; then
+  (cd "$base_dir/git-cl-repo"; git pull -q)
 fi
 
 $repo/git-cl "$@"