Fix Clear-Site-Data WPT that clears active service worker.

A service worker was handling the network request for an iframe page
load. That load also cleared storage (and service workers) via Clear-
Site-Data. This interrupted the page load and prevented the test from
completing.

Specifically, 'support/echo-clear-site-data.py' was returning
[Clear-Site-Data: "storage"] which clobbered the service worker which
was registered for 'support/' which prevented the subload of
'support/test_utils.sub.js'.

The solution is to narrow the scope of the service worker so that it
doesn't apply to the page the iframe is loading.

Bug: 1198698
Change-Id: I6724f5ef8e2140d031b6c570b9c708359a97d140
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4334942
Reviewed-by: Ayu Ishii <[email protected]>
Commit-Queue: Evan Stade <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1116968}

clear-site-data/storage.https.html

@@ -35,7 +35,7 @@
           .then(() => {
             return new Promise(function(resolve, reject) {
               promise_test(function(t) {
-                return navigator.serviceWorker.getRegistration("support/").then(function(reg) {
+                return navigator.serviceWorker.getRegistration("support/page_using_service_worker.html").then(function(reg) {
                   return wait_for_state(t, reg.installing || reg.waiting || reg.active, 'activated');
                 }).then(resolve, reject);
               });

clear-site-data/support/test_utils.sub.js

@@ -121,7 +121,7 @@ var TestUtils = (function() {
       "add": function() {
         return navigator.serviceWorker.register(
             "support/service_worker.js",
-            { scope: "support/"});
+            { scope: "support/page_using_service_worker.html"});
       },
       "isEmpty": function() {
         return new Promise(function(resolve, reject) {