depot_tools: add infra_paths recipe module for infra-specific paths

recipe_modules/gclient/example.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.
 
 DEPS = [
   'gclient',
+  'infra_paths',
   'recipe_engine/path',
   'recipe_engine/properties',
 ]
 
 
 TEST_CONFIGS = [
   'android',
   'android_bare',
   'blink',
   'blink_or_chromium',
@@ skipping 57 matching lines @@
   soln.url = 'svn://svn.chromium.org/blink/trunk'
   bl_cfg.revisions['third_party/WebKit'] = '123'
 
   # Use safesync url for lkgr.
   soln.safesync_url = 'https://blink-status.appspot.com/lkgr'
 
   bl_cfg.got_revision_mapping['src/blatley'] = 'got_blatley_revision'
   api.gclient.checkout(
       gclient_config=bl_cfg,
       with_branch_heads=True,
-      cwd=api.path['slave_build'].join('src', 'third_party'))
+      cwd=api.infra_paths['slave_build'].join('src', 'third_party'))
 
   api.gclient.break_locks()
 
   del api.gclient.spec_alias
 
   api.gclient.runhooks()
 
   assert not api.gclient.is_blink_mode
 
 
 def GenTests(api):
   yield api.test('basic')
 
   yield api.test('revision') + api.properties(revision='abc')
 
   yield api.test('tryserver') + api.properties.tryserver()