Allow fallback from https to http for component update checks.

components/update_client/update_checker.h

Index: components/update_client/update_checker.h
diff --git a/components/update_client/update_checker.h b/components/update_client/update_checker.h
index 1de7f0cf79da5454e619ffdfaae4ae975056f750..1f0eb99389c62b5f5200064894870068f6ebd158 100644
--- a/components/update_client/update_checker.h
+++ b/components/update_client/update_checker.h
@@ -25,7 +25,9 @@ struct CrxUpdateItem;
 class UpdateChecker {
  public:
   using UpdateCheckCallback =
-      base::Callback<void(int error, const UpdateResponse::Results& results)>;
+      base::Callback<void(int error,
+                          const UpdateResponse::Results& results,
+                          int retry_after_sec)>;
 
   using Factory =
       scoped_ptr<UpdateChecker> (*)(const scoped_refptr<Configurator>& config);