Introduce different repo types (git and gitiles)

recipe_engine/remote_run.py

Index: recipe_engine/remote_run.py
diff --git a/recipe_engine/remote_run.py b/recipe_engine/remote_run.py
index 8b6e7fe8bcbfd616da78292b841465977ae8c72a..23a9e5a98b65fd65d822c757c925364d1acc5539 100644
--- a/recipe_engine/remote_run.py
+++ b/recipe_engine/remote_run.py
@@ -36,12 +36,12 @@ def main(args):
     checkout_dir = os.path.join(args.workdir, 'checkout')
     if args.use_gitiles:
       args.revision = args.revision or 'HEAD'
-      fetch.ensure_gitiles_checkout(
-          args.repository, args.revision, checkout_dir, allow_fetch=True)
+      backend = fetch.GitilesBackend()
     else:
       args.revision = args.revision or 'FETCH_HEAD'
-      fetch.ensure_git_checkout(
-          args.repository, args.revision, checkout_dir, allow_fetch=True)
+      backend = fetch.GitBackend()
+    backend.checkout(
+        args.repository, args.revision, checkout_dir, allow_fetch=True)
     recipes_cfg = package.ProtoFile(
         package.InfraRepoConfig().to_recipes_cfg(checkout_dir))
     cmd = [