The error event on `<source>` elements doesn't work. Looking at #4370, it seems like there is an `onError` for `<video>` but I can't tell if that's supposed to work for `<source>` too.

The error event is useful so I can deduce which format the browser is using.

ReactDOM.unmountComponentAtNode(container);
      expect(
        EventPluginHub.getListener(inst, 'onClick')
      ).toBe(undefined);
    });
    it('should clean up input value tracking', function() {
      var container = document.createElement('div');
      var node = ReactDOM.render(<input type="text" defaultValue="foo"/>, container);
      var tracker = inputValueTracking._getTrackerFromNode(node);
      spyOn(tracker, 'stopTracking');
      ReactDOM.unmountComponentAtNode(container);
      expect(tracker.stopTracking.calls.count()).toBe(1);
    });
    it('should clean up input textarea tracking', function() {
      var container = document.createElement('div');
      var node = ReactDOM.render(<textarea defaultValue="foo"/>, container);
      var tracker = inputValueTracking._getTrackerFromNode(node);
      spyOn(tracker, 'stopTracking');
      ReactDOM.unmountComponentAtNode(container);
      expect(tracker.stopTracking.calls.count()).toBe(1);
    });
    it('unmounts children before unsetting DOM node info', function() {
      var Inner = React.createClass({
        render: function() {
          return <span />;
        },
        componentWillUnmount: function() {
          
          expect(ReactDOM.findDOMNode(this).nodeName).toBe('SPAN');
        },