Allow empty commits in presubmit recipe.

Bug:1415507
Recipe-Nontrivial-Roll: build
Change-Id: I6f9833603b2fd1cad0665da762e0a2cd47d4fabd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4547402
Auto-Submit: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

recipes/README.recipes.md

@@ -758,7 +758,7 @@ Raises:
 
 Returns a presubmit step.
 
-— **def [execute](/recipes/recipe_modules/presubmit/api.py#101)(self, bot_update_step, skip_owners=False, run_all=False):**
+— **def [execute](/recipes/recipe_modules/presubmit/api.py#102)(self, bot_update_step, skip_owners=False, run_all=False):**
 
 Runs presubmit and sets summary markdown if applicable.
 

recipes/recipe_modules/presubmit/api.py

@@ -86,6 +86,7 @@ class PresubmitApi(recipe_api.RecipeApi):
                    '-c',
                    'user.name=The Commit Bot',
                    'commit',
+                   '--allow-empty',
                    '-a',
                    '-m',
                    'Committed patch',