See the original report in https://github.com/facebook/react/issues/10772#issuecomment-333242375.

The problem is that SVG is case sensitive, and so naïvely setting `tabIndex` and relying on insensitivity won't work with it.

The good news is it seems like `tabindex` is the only valid [SVG attribute](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute) with this problem. We just missed it because it applies both to HTML and SVG.

I think the fix is to add it back to the whitelist. 
return {foo: 'bar'};
          }
        }
        return render(<MyComponent />);
      },
      'MyComponent.getChildContext(): childContextTypes must be defined ' +
        'in order to use getChildContext().',
    );
    itThrowsWhenRendering(
      'if getChildContext returns a value not in childContextTypes',
      render => {
        class MyComponent extends React.Component {
          render() {
            return <div />;
          }
          getChildContext() {
            return {value1: 'foo', value2: 'bar'};
          }
        }
        MyComponent.childContextTypes = {value1: PropTypes.string};
        return render(<MyComponent />);
      },
      'MyComponent.getChildContext(): key "value2" is not defined in childContextTypes.',
    );
  });
  describe('refs', function() {
    it('should not run ref code on server', async () => {
      let refCount = 0;
      class RefsComponent extends React.Component {