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

content/browser/service_worker/service_worker_provider_host.h

Index: content/browser/service_worker/service_worker_provider_host.h
diff --git a/content/browser/service_worker/service_worker_provider_host.h b/content/browser/service_worker/service_worker_provider_host.h
index d8481e133609e4b4f032970798635da71bbec293..0f8d10cf5fcdb8980840d535c7a2505ee19c16e0 100644
--- a/content/browser/service_worker/service_worker_provider_host.h
+++ b/content/browser/service_worker/service_worker_provider_host.h
@@ -93,6 +93,10 @@ class CONTENT_EXPORT ServiceWorkerProviderHost
   void PostMessage(const base::string16& message,
                    const std::vector<int>& sent_message_port_ids);
 
+  // Returns true if the context referred to by this host (i.e. |context_|) is
+  // still alive.
+  bool IsAlive();
+
  private:
   const int process_id_;
   const int provider_id_;