Move recipe engine to third_party/recipe_engine.

scripts/slave/recipe_modules/webrtc/config.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.
 
-from slave.recipe_config import config_item_context, ConfigGroup
-from slave.recipe_config import Static
+from recipe_engine.config import config_item_context, ConfigGroup
+from recipe_engine.config import Static
 
 
 def BaseConfig(PERF_ID=None, PERF_CONFIG=None, TEST_SUITE=None, **_kwargs):
   return ConfigGroup(
     PERF_ID = Static(PERF_ID),
     PERF_CONFIG = Static(PERF_CONFIG),
     TEST_SUITE = Static(TEST_SUITE),
   )
 
 VAR_TEST_MAP = {
   'PERF_ID': (None, 'perf-id'),
   'PERF_CONFIG': (None, '{}', '{"a_default_rev": "r_webrtc_rev"}'),
 }
 
 def TEST_NAME_FORMAT(kwargs):
   return 'webrtc'  # pragma: no cover
 
 config_ctx = config_item_context(BaseConfig, VAR_TEST_MAP, TEST_NAME_FORMAT)
 
 # Only exists to be able to set the PERF_ID and PERF_CONFIG configurations.
 @config_ctx()
 def webrtc(c):
   pass