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 d6f1ec8306ebab42e9090dbc9ab9f9b734d61852..31f4a372b1bd7633651c8f160266267bbb26d3dd 100644
--- a/content/browser/service_worker/service_worker_provider_host.h
+++ b/content/browser/service_worker/service_worker_provider_host.h
@@ -94,6 +94,10 @@ class CONTENT_EXPORT ServiceWorkerProviderHost
   // versions.
   bool ValidateVersionForAssociation(ServiceWorkerVersion* version);
 
+  // Returns true if the context referred to by this host (i.e. |context_|) is
+  // still alive.
+  bool IsContextAlive();
+
   // Dispatches message event to the document.
   void PostMessage(const base::string16& message,
                    const std::vector<int>& sent_message_port_ids);