There are couple of bugs I noticed:

1. There's a typo in filter comparison code in browser process:
void EventRouter::RemoveFilterFromEvent(const std::string& event_name,
                                        const std::string& extension_id,
                                        const DictionaryValue* filter) {
...

  for (size_t i = 0; i < filter_list->GetSize(); i++) {
    DictionaryValue* filter = NULL;
    CHECK(filter_list->GetDictionary(i, &filter));
    if (filter->Equals(filter)) {  <- ###
      filter_list->Remove(i, NULL);
      break;
    }
  }
}


2. Filtered events are written in ExtensionPrefs under kFilteredEvents key.
But there's a bug  EventRouter::RemoveFilterFromEvent code that doesn't
read the entries properly if an event has "." in its name (which is most
events?)

void EventRouter::RemoveFilterFromEvent(const std::string& event_name,
                                        const std::string& extension_id,
                                        const DictionaryValue* filter) {
...
  if (!filtered_events ||
      !filtered_events->GetList(event_name, &filter_list)) { <- ###
...
}

<- ### needs to be GetListWithoutPathExpansion instead.