Let user know when depot_tools is being updated.

R=gavinmak@google.com

Change-Id: Ieacc0cbe21a5b7216bb8057b3a81139f2d2c608e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3556588
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

update_depot_tools

@@ -125,6 +125,7 @@ function update_git_repo {
 
 # Update git checkouts.
 if [ "X$DEPOT_TOOLS_UPDATE" != "X0" ]; then
+  echo "Updating depot_tools..."
   if [ -e "$base_dir/.git" ]; then
     cd "$base_dir"
     update_git_repo