Add simple depends_on API.

recipe_engine/recipe_api.py

 # Copyright 2013-2015 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 __future__ import absolute_import
 import contextlib
 import keyword
 import re
 import types
 
@@ skipping 436 matching lines @@
   @property
   def name(self):
     return self._module.NAME
 
 
 class RecipeApi(RecipeApiPlain):
   __metaclass__ = RecipeApiMeta
 
 
 class RecipeScriptApi(RecipeApiPlain, ModuleInjectionSite):
-  pass
+  def depend_on(self, recipe, properties, **kwargs):

[luqui, 2015/11/20 01:07:02]

It just occurred to me -- what if a module wants to depend on a recipe?  Should
this be part of RecipeApiPlain instead?

[iannucci, 2015/11/20 02:00:18]

Yes, we should definitely think about this use case

[martiniss, 2015/11/23 22:05:07]

I don't want to have this be a feature for now. If we really want this in the
future, we can easily move the code. 

+    return self._engine.depend_on(recipe, properties, **kwargs)
 
+  def depend_on_test(self, recipe, properties, value, **kwargs):

[luqui, 2015/11/20 01:07:02]

Unused function?

[martiniss, 2015/11/23 22:05:07]

Yes, whoops. Good catch.

+    return self._engine.depend_on_test(recipe, properties, value, **kwargs)
 
 # This is a sentinel object for the Property system. This allows users to
 # specify a default of None that will actually be respected.
 PROPERTY_SENTINEL = object()
 
 class BoundProperty(object):
   """
   A bound, named version of a Property.
 
   A BoundProperty is different than a Property, in that it requires a name,
@@ skipping 159 matching lines @@
     """
     Gets the BoundProperty version of this Property. Requires a name.
     """
     return BoundProperty(
         self._default, self.help, self.kind, name, property_type, module,
         self.param_name)
 
 class UndefinedPropertyException(TypeError):
   pass