Fix how revision_cp is obtained in chromedriver recipe.

scripts/slave/recipes/chromedriver.py

 # Copyright 2016 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.
 
 from recipe_engine import recipe_api
 from recipe_engine.types import freeze
 
 DEPS = [
   'adb',
   'archive',
@@ skipping 50 matching lines @@
   api.bot_update.ensure_checkout()
   api.chromium_android.clean_local_files()
   api.chromium.runhooks()
   api.chromium_android.run_tree_truth()
 
   api.archive.download_and_unzip_build(
       step_name='extract build',
       target=api.chromium.c.BUILD_CONFIG,
       build_url=None,
       build_archive_url=api.properties.get('parent_build_archive_url'))
-  commit_position = api.commit_position.parse_revision(
-      api.properties['got_revision_cp'])
+  revision_cp = api.bot_update.last_returned_properties['got_revision_cp']
+  commit_position = api.commit_position.parse_revision(revision_cp)
 
   api.chromium_android.common_tests_setup_steps()
   if builder['install_apks']:
     for apk in builder['install_apks']:
       api.chromium_android.adb_install_apk(apk)
   api.chromedriver.download_prebuilts()
 
   passed = True
   try:
     api.chromedriver.run_all_tests(
@@ skipping 25 matching lines @@
           '%s_test_failure' % sanitize('Android ChromeDriver Tests (dbg)')) +
       api.properties.generic(
           buildername='Android ChromeDriver Tests (dbg)',
           slavename='slavename',
           mastername='chromium.fyi') +
       api.properties(
           parent_build_archive_url='gs://test-domain/test-archive.zip',
           got_revision='4f4b02f6b7fa20a3a25682c457bbc8ad589c8a00',
           got_revision_cp='refs/heads/master@{#333333}') +
       api.step_data('java_tests(chrome_stable)', retcode=1))