Make git.checkout return the commit hash.

recipe_modules/git/api.py

Index: recipe_modules/git/api.py
diff --git a/recipe_modules/git/api.py b/recipe_modules/git/api.py
index 3832fc3779e7f52e4077969b310064fe13844c09..217dfe8100b0f431c047509b2aac1fc78ca04d4a 100644
--- a/recipe_modules/git/api.py
+++ b/recipe_modules/git/api.py
@@ -140,7 +140,13 @@ class GitApi(recipe_api.RecipeApi):
       file_name (str): optional path to a single file to checkout.
       submodule_update_recursive (bool): if True, updates submodules
           recursively.
+
+    Returns: If set_got_revision is True and the checkout was successful, this

[dnj, 2016/02/12 21:54:45]

Why not always return it, even if set_got_revision is not True?

+      returns the commit hash of the checked-out-repo. Otherwise this returns
+      None.
     """
+    retVal = None
+
     # TODO(robertocn): Break this function and refactor calls to it.
     #     The problem is that there are way too many unrealated use cases for
     #     it, and the function's signature is getting unwieldy and its body
@@ -256,6 +262,7 @@ class GitApi(recipe_api.RecipeApi):
 
       if rev_parse_step.presentation.status == 'SUCCESS':
         sha = rev_parse_step.stdout.strip()
+        retVal = sha
         rev_parse_step.presentation.properties['got_revision'] = sha
 
     clean_args = list(itertools.chain(
@@ -281,6 +288,8 @@ class GitApi(recipe_api.RecipeApi):
         cwd=dir_path,
         can_fail_build=can_fail_build)
 
+    return retVal
+
   def get_timestamp(self, commit='HEAD', test_data=None, **kwargs):
     """Find and return the timestamp of the given commit."""
     step_test_data = None