Fixed clean URLs for GCS file system provider in the documentation server.

chrome/common/extensions/docs/server2/gcs_file_system.py

Index: chrome/common/extensions/docs/server2/gcs_file_system.py
diff --git a/chrome/common/extensions/docs/server2/gcs_file_system.py b/chrome/common/extensions/docs/server2/gcs_file_system.py
index 909377ad8046785115e1302104ea07f769397b43..355728f6e290e9c3f0fb3db5af5ea4f015135805 100644
--- a/chrome/common/extensions/docs/server2/gcs_file_system.py
+++ b/chrome/common/extensions/docs/server2/gcs_file_system.py
@@ -39,8 +39,8 @@ def _ReadFile(filename):
 def _ListDir(dir_name):
   AssertIsDirectory(dir_name)
   try:
-    files = cloudstorage_api.listbucket('/' + dir_name)
-    return [os_path.filename.lstrip('/') for os_path in files]
+    files = cloudstorage_api.listbucket('/' + dir_name, delimiter='/')
+    return [os_path.filename.lstrip('/')[len(dir_name):] for os_path in files]
   except errors.Error:
     raise FileNotFoundError('cloudstorage.listbucket failed for %s: %s' %
                             (dir_name, traceback.format_exc()))