Warn when fsmonitor is enabled and git submodules are used

Change-Id: I181bf180f762282d5b4bc614d12a91125f56e063
Bug: 1475405
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4814429
Auto-Submit: Aravind Vasudevan <aravindvasudev@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
diff --git a/git_cl.py b/git_cl.py
index b0f7efb..0b2d34f 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -4738,6 +4738,11 @@
                    if opt.help != optparse.SUPPRESS_HELP))
     return
 
+  # TODO(crbug.com/1475405): Warn users if the project uses submodules and
+  # they have fsmonitor enabled.
+  if os.path.isfile('.gitmodules'):
+    git_common.warn_submodule()
+
   if git_common.is_dirty_git_tree('upload'):
     return 1