Add Paths as first-class types in configs.

scripts/slave/recipes/polymer.py

 # Copyright (c) 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.
 
 
 DEPS = [
   'gclient',
   'git',
   'path',
   'platform',
@@ skipping 34 matching lines @@
       'submodule update', api.path.depot_tools('gclient.py'),
       ['recurse', 'git', 'submodule', 'update', '--init', '--recursive'])
 
   return (
       api.gclient.checkout(cfg),
       submodule_command
   )
 
 
 def GenSteps(api):
-
   yield _CheckoutSteps(api)
   this_repo = api.properties['buildername'].split()[0]
-  api.path.choose_checkout(api.path.slave_build(this_repo))
+  api.path.set_dynamic_path('checkout', api.path.slave_build(this_repo))
 
   tmp_path = ''
   tmp_args = []
   if not api.platform.is_win:
     tmp_path = api.path.slave_build('.tmp')
     yield api.path.makedirs('tmp', tmp_path)
     tmp_args = ['--tmp', tmp_path]
 
   cmd_suffix = ''
   node_env = {}
@@ skipping 11 matching lines @@
       'IE_BIN':
         api.path.join('C:', api.path.sep, 'Program Files', 'Internet Explorer',
                       'iexplore.exe'),
     }
 
   test_prefix = []
   if api.platform.is_linux:
     test_prefix = ['xvfb-run']
 
   yield api.step('update-install', ['npm' + cmd_suffix, 'install'] + tmp_args,
-                 cwd=api.path.checkout(), env=node_env)
+                 cwd=api.path.checkout, env=node_env)
 
   yield api.step('test', test_prefix + ['grunt' + cmd_suffix,
-                 'test-buildbot'], cwd=api.path.checkout(),
+                 'test-buildbot'], cwd=api.path.checkout,
                  env=node_env, allow_subannotations=True)
 
 
 def GenTests(api):
   # Test paths and commands on each platform.
   for plat in ('mac', 'linux', 'win'):
     yield (
       api.test('polymer-%s' % plat) +
       api.properties.scheduled(
         repository='https://github.com/Polymer/polymer',
         buildername='polymer %s' % plat,
       ) +
       api.platform.name(plat)
     )
 
   # Make sure the steps are right for deps-triggered jobs.
   yield (
     api.test('polymer-from-platform') +
     api.properties.scheduled(
       repository='https://github.com/Polymer/platform',
       buildername='polymer linux',
       scheduler='polymer-platform'
     )
   )