chromite recipe: Add warm cache flag support.

scripts/slave/recipe_modules/chromite/api.py

Index: scripts/slave/recipe_modules/chromite/api.py
diff --git a/scripts/slave/recipe_modules/chromite/api.py b/scripts/slave/recipe_modules/chromite/api.py
index b8706a9f204729735d1057f9e80aed3038b95be6..b7da9be2e63641f0e9ce572e9a6ba7e9cd761aa3 100644
--- a/scripts/slave/recipe_modules/chromite/api.py
+++ b/scripts/slave/recipe_modules/chromite/api.py
@@ -348,6 +348,8 @@ class ChromiteApi(recipe_api.RecipeApi):
       cbb_args.extend(['--chrome_version', self.c.cbb.chrome_version])
     if self.c.cbb.config_repo:
       cbb_args.extend(['--config_repo', self.c.cbb.config_repo])
+    if self.c.repo_cache_dir and self.c.cbb.supports_repo_cache:
+      cbb_args.extend(['--repo-cache', self.c.repo_cache_dir])
 
     # Set the build ID, if specified.
     if self.c.cbb.build_id: