WebRTC: Fallback for working_dir in symlink cleaning

scripts/slave/recipe_modules/webrtc/api.py

Index: scripts/slave/recipe_modules/webrtc/api.py
diff --git a/scripts/slave/recipe_modules/webrtc/api.py b/scripts/slave/recipe_modules/webrtc/api.py
index 5d9cfc81b69d3d86f6fa446f7adecf8e4316968c..84e4a2785c8c8a4e8bc67bb423ad85773546c6cf 100644
--- a/scripts/slave/recipe_modules/webrtc/api.py
+++ b/scripts/slave/recipe_modules/webrtc/api.py
@@ -178,13 +178,15 @@ class WebRTCApi(recipe_api.RecipeApi):
     self._working_dir = self.m.chromium_checkout.get_checkout_dir({})
     if self._working_dir:
       kwargs.setdefault('cwd', self._working_dir)
+    else:
+      self._working_dir = self.m.path['slave_build']
 
     # TODO(kjellander): Deploy at all bots once verified working.
     if self.mastername == 'client.webrtc.fyi':
       # Cleanup symlinks if there are any created.
       self.m.python('clean symlinks',
                     script=self.resource('cleanup_symlinks.py'),
-                    args=[self.m.path['slave_build']],
+                    args=[self._working_dir],
                     infra_step=True)
 
     update_step = self.m.bot_update.ensure_checkout(**kwargs)