Allow banners to trigger on sites which don't register a service worker onload.

chrome/test/data/banners/main.js

Index: chrome/test/data/banners/main.js
diff --git a/chrome/test/data/banners/main.js b/chrome/test/data/banners/main.js
index 484e7b44ecf4a84f0ba85e5ada6cf545f625f9e7..f24ce64f24d0ca6d9668bc093603d5c8e5ec8ad2 100644
--- a/chrome/test/data/banners/main.js
+++ b/chrome/test/data/banners/main.js
@@ -20,3 +20,11 @@ function addManifestLinkTag() {
   linkTag.href = manifestUrl;
   document.head.append(linkTag);
 }
+
+function getSwDelay() {
+  // Allow the test page to set a custom delay (required since desktop is
+  // faster than Android and hence needs a longer delay).
+  var url = window.location.href;
+  var swDelayIndex = url.indexOf("?swdelay=");
+  return (swDelayIndex >= 0) ? url.slice(swDelayIndex + 9) : 300;
+}