Have LazyBackgroundTaskQueue notify consumers when the transient page fails to

chrome/browser/extensions/extension_message_service.cc

Index: chrome/browser/extensions/extension_message_service.cc
diff --git a/chrome/browser/extensions/extension_message_service.cc b/chrome/browser/extensions/extension_message_service.cc
index 1cf132a22ba54a42a2b791ad4927fe815d843502..ccb555e958f3f27a2915397a4b5acd945f0aa62a 100644
--- a/chrome/browser/extensions/extension_message_service.cc
+++ b/chrome/browser/extensions/extension_message_service.cc
@@ -442,6 +442,9 @@ void ExtensionMessageService::PendingOpenChannel(
     const OpenChannelParams& params_in,
     int source_process_id,
     ExtensionHost* host) {
+  if (!host)
+    return;  // TODO(mpcomplete): notify source of disconnect?
+
   // Re-lookup the source process since it may no longer be valid.
   OpenChannelParams params = params_in;
   params.source = content::RenderProcessHost::FromID(source_process_id);