service worker: Wait for inflight requests before activating

third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/mint-new-worker.php

+<?php
+// Mint a new worker each load.
+header("Cache-Control: no-cache, must-revalidate");
+header("Pragma: no-cache");
+header('Content-Type:application/javascript');
+echo "// " . microtime() . "\n";
+
+if ($_SERVER['QUERY_STRING'] == 'skip-waiting') {
+  echo "skipWaiting();\n";
+}
+?>
+onactivate = (e) => e.waitUntil(clients.claim());
+
+var resolve_wait_until;
+var wait_until = new Promise(resolve => {
+    resolve_wait_until = resolve;
+  });
+onmessage = (e) => {
+    if (e.data == 'wait')
+      e.waitUntil(wait_until);
+    if (e.data == 'go')
+      resolve_wait_until();
+  };