code: function (topLevelType, targetInst, nativeEvent, nativeEventTarget) {
      var events;
      var plugins = EventPluginRegistry_1.plugins;
      for (var i = 0; i < plugins.length; i++) {
        // Not every plugin in the ordering may be loaded at runtime.
        var possiblePlugin = plugins[i];
        if (possiblePlugin) {
          var extractedEvents = possiblePlugin.extractEvents(topLevelType, targetInst, nativeEvent, nativeEventTarget);
          if (extractedEvents) {
            events = accumulateInto_1(events, extractedEvents);
          }
        }
      }
      return events;
    }
docs: Allows registered plugins an opportunity to extract events from top-level
  native browser events.
  
  @return {*} An accumulation of synthetic events.
  @internal