webRequest: Check weak ptr before dispatching event

extensions/browser/api/web_request/web_request_api.cc

Index: extensions/browser/api/web_request/web_request_api.cc
diff --git a/extensions/browser/api/web_request/web_request_api.cc b/extensions/browser/api/web_request/web_request_api.cc
index 76db07fe55227c27b68a4d37a37fc19722873318..532e43d266d8d7e620c459d6aba532fdb0d36a71 100644
--- a/extensions/browser/api/web_request/web_request_api.cc
+++ b/extensions/browser/api/web_request/web_request_api.cc
@@ -1072,6 +1072,9 @@ void ExtensionWebRequestEventRouter::DispatchEventToListeners(
         continue;
     }
 
+    if (!listener->ipc_sender.get())
+      continue;
+
     // Filter out the optional keys that this listener didn't request.
     scoped_ptr<base::ListValue> args_filtered(new base::ListValue);
     args_filtered->Append(