Use iife format when bundling assets to avoid naming collision

Bug: Issue 12744
Change-Id: If6a53d58228e34f724a59980443a9bdcf8ec5dc9

BUILD

diff --git a/BUILD b/BUILD
index 7008531..c982cdb 100644
--- a/BUILD
+++ b/BUILD
@@ -49,6 +49,7 @@
     entry_point = "gr-delete-repo/plugin.js",
     rollup_bin = "//tools/node_tools:rollup-bin",
     sourcemap = "hidden",
+    format = "iife",
     deps = [
         "@tools_npm//rollup-plugin-node-resolve",
     ],