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.

);
      expect(console.error.calls.count()).toBe(1);
      expect(console.error.calls.argsFor(0)[0]).toContain('contentEditable');
    });
    it('should validate against invalid styles', function() {
      ReactDOM.render(<div></div>, container);
      expect(function() {
        ReactDOM.render(<div style={1}></div>, container);
      }).toThrowError(
        'The `style` prop expects a mapping from style properties to values, ' +
        'not a string. For example, style={{marginRight: spacing + \'em\'}} ' +
        'when using JSX.'
      );
    });
    it('should report component containing invalid styles', function() {
      var Animal = React.createClass({
        render: function() {
          return <div style={1}></div>;
        },
      });
      expect(function() {
        ReactDOM.render(<Animal/>, container);
      }).toThrowError(
        'The `style` prop expects a mapping from style properties to values, ' +
        'not a string. For example, style={{marginRight: spacing + \'em\'}} ' +
        'when using JSX. This DOM node was rendered by `Animal`.'
      );
    });
    it('should properly escape text content and attributes values', function() {
      expect(