Add LayoutTests for the fixed multithread GC bug of ServiceWorker Navigation Preload

third_party/WebKit/LayoutTests/http/tests/serviceworker/navigation-preload/chromium/resources/preload-response-after-gc-worker.js

+
+self.addEventListener('activate', e => {
+    e.waitUntil(self.registration.navigationPreload.enable());
+  });
+
+self.addEventListener('fetch', e => {
+    internals.collectGarbage();
+    // Sleeps 100 ms.
+    var end = Date.now() + 100;
+    while (Date.now() < end);
+    e.respondWith(new Response("hello"));
+  });