cherry-pick(release-1.16): keep sw alive

PR #9725
SHA e271045

Author: pavelfeldman

packages/playwright-core/src/web/traceViewer/index.tsx

@@ -29,5 +29,7 @@ import '../common.css';
       navigator.serviceWorker.oncontrollerchange = () => f();
     });
   }
+  // Keep SW running.
+  setInterval(function() { fetch('ping'); }, 10000);
   ReactDOM.render(<Workbench/>, document.querySelector('#root'));
 })();

packages/playwright-core/src/web/traceViewer/sw.ts

@@ -56,8 +56,12 @@ async function doFetch(event: FetchEvent): Promise<Response> {
     const url = new URL(request.url);
 
     const relativePath = url.pathname.substring(scopePath.length - 1);
-    if (relativePath === '/context') {
+    if (relativePath === '/ping') {
       await gc();
+      return new Response(null, { status: 200 });
+    }
+
+    if (relativePath === '/context') {
       const traceModel = await loadTrace(traceUrl, event.clientId);
       return new Response(JSON.stringify(traceModel!.contextEntry), {
         status: 200,