Handle updating depot_tools repos that are git cloned.

update_depot_tools

 #!/usr/bin/env bash
 # Copyright (c) 2011 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.
 
 # This script will try to sync the bootstrap directories and then defer control.
 
 if [ "$USER" == "root" ];
 then
   echo Running depot tools as root is sad.
@@ skipping 45 matching lines @@
 
   GITV="${GITV#* version }"   # git svn --version has extra output to remove.
   GITV="${GITV% (svn*}"
   local GITD=( ${GITV//./ } ) # Split version number into decimals
   if ((GITD[0] < 1 || (GITD[0] == 1 && GITD[1] < 6) )); then
     echo "git version is ${GITV}, please update to a version later than 1.6"
     exit 1
   fi
 }
 
+function is_git_clone_repo {
+  "$GIT" config remote.origin.fetch > /dev/null
+}
+
+function update_git_repo {
+  if is_git_clone_repo; then
+    git fetch -q origin > /dev/null
+    git rebase -q origin > /dev/null
+    return 0
+  fi
+
+  test_git_svn
+  # work around a git-svn --quiet bug
+  OUTPUT=`"$GIT" svn rebase -q -q`
+  if [[ ! "$OUTPUT" == *Current.branch* ]]; then
+    echo $OUTPUT 1>&2
+  fi
+  return 0
+}
+
 # Get the current SVN revision.
 get_svn_revision() {
   LANGUAGE=C "$SVN" info "$base_dir" | \
       awk -F': ' '{ if ($1 == "Last Changed Rev") { print $2 }}'
 }
 
 # Update git checkouts.
 if [ "X$DEPOT_TOOLS_UPDATE" != "X0" -a -e "$base_dir/.git" ]
 then
   cd $base_dir
-  test_git_svn
-  # work around a git-svn --quiet bug
-  OUTPUT=`"$GIT" svn rebase -q -q`
-  if [[ ! "$OUTPUT" == *Current.branch* ]]; then
-    echo $OUTPUT 1>&2
-  fi
+  update_git_repo
   cd - > /dev/null
 fi
 
 # We're on POSIX. We can now safely look for svn checkout.
 if [ "X$DEPOT_TOOLS_UPDATE" != "X0" -a -e "$base_dir/.svn" ]
 then
   # Update the root directory to stay up-to-date with the latest depot_tools.
   BEFORE_REVISION=$(get_svn_revision)
   "$SVN" -q up "$base_dir"
   AFTER_REVISION=$(get_svn_revision)
   if [[ "$BEFORE_REVISION" != "$AFTER_REVISION" ]]; then
     echo "Depot Tools has been updated to revision $AFTER_REVISION." 1>&2
   fi
 fi
 
 find "$base_dir" -iname "*.pyc" -exec rm {} \;