Have LazyBackgroundTaskQueue notify consumers when the transient page fails to

chrome/browser/extensions/extension_event_router.cc

Index: chrome/browser/extensions/extension_event_router.cc
diff --git a/chrome/browser/extensions/extension_event_router.cc b/chrome/browser/extensions/extension_event_router.cc
index 78993ed01b0f5d308b66a43bcad3598aa5ecd185..908c06c49e977666fc967c3287820c5ea7e0af65 100644
--- a/chrome/browser/extensions/extension_event_router.cc
+++ b/chrome/browser/extensions/extension_event_router.cc
@@ -423,6 +423,9 @@ void ExtensionEventRouter::OnExtensionEventAck(
 
 void ExtensionEventRouter::DispatchPendingEvent(
     const linked_ptr<ExtensionEvent>& event, ExtensionHost* host) {
+  if (!host)
+    return;
+
   ListenerProcess listener(host->render_process_host(),
                            host->extension()->id());
   if (listeners_[event->event_name].count(listener) > 0u)