Move recipe engine to third_party/recipe_engine.

scripts/slave/recipe_modules/buildbot/api.py

 # Copyright 2014 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 import recipe_api
+from recipe_engine import recipe_api
 
 class BuildbotApi(recipe_api.RecipeApi):
   def prep(self):
     """Prepatory steps for buildbot based recipes."""
     # TODO(iannucci): Also do taskkill?
     self.m.python(
       'cleanup temp',
       self.m.path['build'].join('scripts', 'slave', 'cleanup_temp.py')
     )
 
   def copy_parent_got_revision_to_got_revision(self):
     """Returns a step which copies the 'parent_got_revision' build property
     to the 'got_revision' build property. This is needed for recipes which
     use isolates for testing and which skip the src/ checkout."""
 
     result = self.m.python.inline(
       'copy parent_got_revision to got_revision',
       'exit()')
     result.presentation.properties['got_revision'] = (
         self.m.properties['parent_got_revision'])