Add Paths as first-class types in configs.

scripts/slave/recipe_modules/gclient/config.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.
 
 import types
 
 from slave.recipe_config import config_item_context, ConfigGroup, BadConf
 from slave.recipe_config import ConfigList, Dict, Single, Static, Set, List
 
 def BaseConfig(USE_MIRROR=True, GIT_MODE=False, CACHE_DIR=None, **_kwargs):
@@ skipping 11 matching lines @@
         custom_vars = Dict(value_type=basestring),
         safesync_url = Single(basestring, required=False),
 
         revision = Single(basestring, required=False, hidden=True),
       )
     ),
     deps_os = Dict(value_type=basestring),
     hooks = List(basestring),
     target_os = Set(basestring),
     target_os_only = Single(bool, empty_val=False, required=False),
-    checkouts = List(basestring, hidden=True),
     cache_dir = Static(cache_dir, hidden=False),
     got_revision_mapping = Dict(hidden=True),
 
     GIT_MODE = Static(bool(GIT_MODE)),
     USE_MIRROR = Static(bool(USE_MIRROR)),
   )
 
 VAR_TEST_MAP = {
   'USE_MIRROR': (True, False),
   'GIT_MODE':   (True, False),
@@ skipping 154 matching lines @@
 
 @config_ctx(config_vars={'GIT_MODE': True})
 def tools_build(c):
   if not c.GIT_MODE:
     raise BadConf('tools_build only supports git')
   s = c.solutions.add()
   s.name = 'build'
   s.url = ChromiumGitURL(c, 'chromium', 'tools', 'build.git')