depot_tools: add infra_paths recipe module for infra-specific paths

recipe_modules/infra_paths/api.py

+# Copyright 2016 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 recipe_engine import recipe_api
+
+
+class InfraPathsApi(recipe_api.RecipeApi):
+  def get_config_defaults(self):
+    return {
+      'PLATFORM': self.m.platform.name,
+      'CURRENT_WORKING_DIR': self.m.path['cwd'],
+      'ROOT': self.m.path['root'],
+    }
+
+  def __init__(self, **kwargs):
+    super(InfraPathsApi, self).__init__(**kwargs)
+    self._config_set = False
+
+  def _lazy_set_config(self):
+    if self._config_set:
+      return
+    self._config_set = True
+
+    path_config = self.m.properties.get('path_config')
+    if path_config in ('kitchen',):
+      self.set_config(path_config)
+    else:
+      self.set_config('buildbot')
+
+  def __getitem__(self, name):
+    self._lazy_set_config()
+    return self.c.paths[name]