ServiceWorker: Confirm the liveness of the associated context before handling message

content/browser/service_worker/service_worker_provider_host.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/service_worker/service_worker_provider_host.h"
 
 #include "base/stl_util.h"
 #include "content/browser/message_port_message_filter.h"
 #include "content/browser/service_worker/service_worker_context_core.h"
 #include "content/browser/service_worker/service_worker_context_request_handler.h"
@@ skipping 126 matching lines @@
                                       &new_routing_ids);
 
   dispatcher_host_->Send(
       new ServiceWorkerMsg_MessageToDocument(
           kDocumentMainThreadId, provider_id(),
           message,
           sent_message_port_ids,
           new_routing_ids));
 }
 
+bool ServiceWorkerProviderHost::IsAlive() {
+  return context_ != NULL;
+}
+
 }  // namespace content