fail gracefully if git map-branches is called in cog

Bug: 339231299
Change-Id: I65c96463be51bb7da32b44c280d75622842612c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5540669
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>

git_map_branches.py

@@ -33,6 +33,7 @@ from git_common import current_branch, upstream, tags, get_branches_info
 from git_common import get_git_version, MIN_UPSTREAM_TRACK_GIT_VERSION, hash_one
 from git_common import get_config, run
 
+import gclient_utils
 import setup_color
 
 from third_party.colorama import Fore, Style
@@ -339,6 +340,10 @@ def print_desc():
 
 @metrics.collector.collect_metrics('git map-branches')
 def main(argv):
+    if gclient_utils.IsEnvCog():
+        print('map-branches command is not supported in non-git environment.',
+              file=sys.stderr)
+        return 1
     setup_color.init()
     if get_git_version() < MIN_UPSTREAM_TRACK_GIT_VERSION:
         print(