build: use class path bases, not strings

scripts/slave/recipe_modules/libyuv/chromium_config.py

 # Copyright 2014 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.config import BadConf
 
 import DEPS
 CONFIG_CTX = DEPS['chromium'].CONFIG_CTX
 from recipe_engine.config_types import Path
 
 
 @CONFIG_CTX(includes=['chromium'])
 def libyuv(c):
   _libyuv_common(c)
 
-  c.runtests.memory_tests_runner = Path('[CHECKOUT]', 'tools',
-                                        'valgrind-libyuv', 'libyuv_tests',
-                                        platform_ext={'win': '.bat',
-                                                      'mac': '.sh',
-                                                      'linux': '.sh'})
+  c.runtests.memory_tests_runner = c.CHECKOUT_PATH.join(
+      'tools', 'valgrind-libyuv', 'libyuv_tests',
+      platform_ext={'win': '.bat', 'mac': '.sh', 'linux': '.sh'})
 
 @CONFIG_CTX(includes=['chromium_clang'])
 def libyuv_clang(c):
   _libyuv_common(c)
 
 @CONFIG_CTX(includes=['android'])
 def libyuv_android(c):
   pass
 
 @CONFIG_CTX(includes=['android_clang'])
@@ skipping 12 matching lines @@
 
   gyp_defs = c.gyp_env.GYP_DEFINES
   gyp_defs['OS'] = c.TARGET_PLATFORM
   if c.TARGET_BITS == 64:
     gyp_defs['target_subarch'] = 'arm64'
 
   _libyuv_common(c)
 
 def _libyuv_common(c):
   c.compile_py.default_targets = ['All']