Recipes: make cwd default to slave_build

scripts/slave/recipe_modules/step/api.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 import recipe_api
 from slave import recipe_util
 
 
 # Inherit from RecipeApiPlain because the only thing which is a step is
 # run_from_dict()
@@ skipping 96 matching lines @@
     if step_count > 1:
       name = "%s (%d)" % (name, step_count)
 
     kwargs['ok_ret'] = ok_ret
     kwargs['infra_step'] = bool(infra_step)
 
     # Obtain information from composite step parent.
     kwargs['name'] = compositor.get_with_context('name', name)
     kwargs['env'] = compositor.get_with_context('env', kwargs.get('env', {}))
 
+    kwargs.setdefault('cwd', self.m.path['slave_build'])
+
     schema = self.make_config()
     schema.set_val(kwargs)
     return self.run_from_dict(self._engine.create_step(schema))
 
   # TODO(martiniss) delete, and make generator_script use **kwargs on step()
   @recipe_api.composite_step
   def run_from_dict(self, dct):
     return self._engine.run_step(dct)