retry on HTTP status 429 "Too Many Requests"

background/update.js

@@ -105,8 +105,10 @@ global API_METHODS
     }
 
     function reportFailure(error) {
-      // retry once if the error is 503 Service Unavailable
-      if (error === 503 && !retrying.has(id)) {
+      if ((
+        error === 503 || // Service Unavailable
+        error === 429    // Too Many Requests
+      ) && !retrying.has(id)) {
         retrying.add(id);
         return new Promise(resolve => {
           setTimeout(() => {