Enforce passing cwd via context rather then api.step kwargs

recipe_modules/step/api.py

Index: recipe_modules/step/api.py
diff --git a/recipe_modules/step/api.py b/recipe_modules/step/api.py
index 8530f6ffdafcd8d71d8595732653e2a08a79fa7c..0620453cc50d86ac054cd0fe1de87d0c59323fc8 100644
--- a/recipe_modules/step/api.py
+++ b/recipe_modules/step/api.py
@@ -77,6 +77,9 @@ class StepApi(recipe_api.RecipeApiPlain):
     """ See recipe_api.py for docs. """
     return recipe_api.context
 
+  def get_context(self):
+    return recipe_api._STEP_CONTEXT
+
   @contextlib.contextmanager
   def nest(self, name):
     """Nest is the high-level interface to annotated hierarchical steps.
@@ -101,7 +104,7 @@ class StepApi(recipe_api.RecipeApiPlain):
     return recipe_api.defer_results
 
   def __call__(self, name, cmd, ok_ret=None, infra_step=False, wrapper=(),
-               timeout=None, cwd=None, env=None, allow_subannotations=None,
+               timeout=None, env=None, allow_subannotations=None,
                trigger_specs=None, stdout=None, stderr=None, stdin=None,
                step_test_data=None):
     """Returns a step dictionary which is compatible with annotator.py.
@@ -141,8 +144,6 @@ class StepApi(recipe_api.RecipeApiPlain):
       Opaque step object produced and understood by recipe engine.
     """
     kwargs = {}
-    if cwd:
-      kwargs['cwd'] = cwd
     if env:
       kwargs['env'] = env
     if allow_subannotations is not None:
@@ -172,7 +173,7 @@ class StepApi(recipe_api.RecipeApiPlain):
     kwargs['ok_ret'] = ok_ret
 
     # Obtain information from composite step parent.
-    compositor = recipe_api._STEP_CONTEXT
+    compositor = self.get_context()
 
     # Calculate our full step name. If a step already has that name, add an
     # index to the end of it.