Make git.checkout return the commit hash.

recipe_modules/git/example.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 DEPS = [
   'git',
   'recipe_engine/path',
   'recipe_engine/platform',
   'recipe_engine/properties',
   'recipe_engine/raw_io',
   'recipe_engine/step',
 ]
 
 
 def RunSteps(api):
   url = 'https://chromium.googlesource.com/chromium/src.git'
 
   # git.checkout can optionally dump GIT_CURL_VERBOSE traces to a log file,
   # useful for debugging git access issues that are reproducible only on bots.
   curl_trace_file = None
   if api.properties.get('use_curl_trace'):
     curl_trace_file = api.path['slave_build'].join('curl_trace.log')
 
   submodule_update_force = api.properties.get('submodule_update_force', False)
   submodule_update_recursive = api.properties.get('submodule_update_recursive',
           True)
 
   # You can use api.git.checkout to perform all the steps of a safe checkout.
-  api.git.checkout(
+  set_got_revision=api.properties.get('set_got_revision')
+  retVal = api.git.checkout(
       url,
       ref=api.properties.get('revision'),
       recursive=True,
       submodule_update_force=submodule_update_force,
-      set_got_revision=api.properties.get('set_got_revision'),
+      set_got_revision=set_got_revision,
       curl_trace_file=curl_trace_file,
       remote_name=api.properties.get('remote_name'),
       display_fetch_size=api.properties.get('display_fetch_size'),
       file_name=api.properties.get('checkout_file_name'),
       submodule_update_recursive=submodule_update_recursive)
 
+  if set_got_revision:
+    assert retVal == api.properties['expected_got_revision'], (
+      "expected retVal to be %r but was %r" % (
+        api.properties['expected_got_revision'], retVal))
+
   # count_objects shows number and size of objects in .git dir.
   api.git.count_objects(
       name='count-objects',
       can_fail_build=api.properties.get('count_objects_can_fail_build'),
       git_config_options={'foo': 'bar'})
 
   # Get the remote URL.
   api.git.get_remote_url(
       step_test_data=lambda: api.raw_io.test_api.stream_output('foo'))
 
@@ skipping 49 matching lines @@
     api.step_data('git status can_fail_build', retcode=1)
   )
 
   yield (
     api.test('cannot_fail_build') +
     api.step_data('git status cannot_fail_build', retcode=1)
   )
 
   yield (
       api.test('set_got_revision') +
-      api.properties(set_got_revision=True) +
+      api.properties(
+        set_got_revision=True,
+        expected_got_revision="deadbeef",
+      ) +
       api.step_data('set got_revision',
                     stdout=api.raw_io.output('deadbeef'))
   )
 
   yield (
     api.test('rebase_failed') +
     api.step_data('my repo rebase', retcode=1)
   )
 
   yield api.test('remote_not_origin') + api.properties(remote_name='not_origin')
@@ skipping 16 matching lines @@
       api.test('count-objects_with_bad_output_fails_build') +
       api.step_data(
           'count-objects',
           stdout=api.raw_io.output(api.git.count_objects_output('xxx'))) +
       api.properties(count_objects_can_fail_build=True))
   yield (
       api.test('cat-file_test') +
       api.step_data('git cat-file abcdef12345:TestFile',
                     stdout=api.raw_io.output('TestOutput')) +
       api.properties(revision='abcdef12345', cat_file='TestFile'))