blink_downstream: prepare for remote_run conversion

scripts/slave/recipe_modules/chromium_tests/api.py

Index: scripts/slave/recipe_modules/chromium_tests/api.py
diff --git a/scripts/slave/recipe_modules/chromium_tests/api.py b/scripts/slave/recipe_modules/chromium_tests/api.py
index dbb784dde3ebf25faacbfc9c3a3771ad29c77fd1..5d5c101df3cbd5afc97625118cbcdc9b988beb6b 100644
--- a/scripts/slave/recipe_modules/chromium_tests/api.py
+++ b/scripts/slave/recipe_modules/chromium_tests/api.py
@@ -130,24 +130,28 @@ class ChromiumTestsApi(recipe_api.RecipeApi):
       dep = bot_config.get('set_component_rev')
       self.m.gclient.c.revisions[dep['name']] = dep['rev_str'] % component_rev
 
-  def ensure_checkout(self, bot_config, root_solution_revision=None,
-                      force=False):
-    if self.m.platform.is_win:
-      self.m.chromium.taskkill()
-
-    kwargs = {}
+  def get_checkout_dir(self, bot_config):
     try:
       builder_cache = self.m.path['builder_cache']
     except KeyError:  # no-op if builder cache is not set up.
-      pass
+      return None
     else:
       sanitized_buildername = ''.join(
           c if c.isalnum() else '_' for c in self.m.properties['buildername'])
-      checkout_path = builder_cache.join(
+      checkout_dir = builder_cache.join(
           bot_config.get('checkout_dir', sanitized_buildername))
-      self.m.shutil.makedirs('checkout path', checkout_path)
-      kwargs['cwd'] = checkout_path
-      self._working_dir = checkout_path
+      self.m.shutil.makedirs('checkout path', checkout_dir)
+      return checkout_dir
+
+  def ensure_checkout(self, bot_config, root_solution_revision=None,
+                      force=False):
+    if self.m.platform.is_win:
+      self.m.chromium.taskkill()
+
+    kwargs = {}
+    self._working_dir = self.get_checkout_dir(bot_config)
+    if self._working_dir:
+      kwargs['cwd'] = self._working_dir
 
     # Bot Update re-uses the gclient configs.
     update_step = self.m.bot_update.ensure_checkout(