[ServiceWorker] Convert ping-pong IPC into mojo interface ServiceWorkerEventDispatcher

content/browser/service_worker/embedded_worker_test_helper.cc

Index: content/browser/service_worker/embedded_worker_test_helper.cc
diff --git a/content/browser/service_worker/embedded_worker_test_helper.cc b/content/browser/service_worker/embedded_worker_test_helper.cc
index aac27b710297cc8d59d9b653b93149f2e3fabeb1..2c6b1bf30348f1a4d43957ca5fb356e68a5e2895 100644
--- a/content/browser/service_worker/embedded_worker_test_helper.cc
+++ b/content/browser/service_worker/embedded_worker_test_helper.cc
@@ -219,6 +219,8 @@ class EmbeddedWorkerTestHelper::MockServiceWorkerEventDispatcher
     helper_->OnExtendableMessageEventStub(std::move(event), callback);
   }
 
+  void Ping(const PingCallback& callback) override { callback.Run(); }
+
  private:
   base::WeakPtr<EmbeddedWorkerTestHelper> helper_;
   const int thread_id_;