Add simple depends_on API.

recipe_engine/unittests/run_test.py

 #!/usr/bin/env python
 # 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.
 
 import os
 import subprocess
 import sys
 import unittest
 
@@ skipping 53 matching lines @@
     properties = {}
 
     test_data = mock.Mock()
     test_data.enabled = True
     test_data.consumed = False
 
     api = mock.Mock()
     api._engine = mock.Mock()
     api._engine.properties = properties
 
-    engine = recipe_engine.run.RecipeEngine(stream, properties, test_data)
+    engine = recipe_engine.run.RecipeEngine(stream, properties, test_data, None)
 
     class FakeScript(object):
       def run(self, _, __):
         return None
 
     with mock.patch('recipe_engine.run.RecipeEngine._emit_results'):
       with self.assertRaises(AssertionError):
         engine.run(FakeScript(), api)
 
 
-
 if __name__ == '__main__':
   unittest.TestCase.maxDiff = None
   unittest.main()