Currently if React is not loaded, ReactDOM shows this:

<img width="664" alt="screen shot 2017-08-08 at 3 36 52 pm" src="https://user-images.githubusercontent.com/810438/29077217-784c7624-7c4f-11e7-88bc-b055407523a9.png">

We should throw a nicer error message in the entry point I think.
state = {error: null};
        componentDidCatch(error) {
          this.setState({error});
        }
        render() {
          if (this.state.error) {
            return <p {...expectHTML} />;
          }
          return this.props.children;
        }
      }
      assertNamespacesMatch(
        <svg {...expectSVG}>
          <foreignObject {...expectSVG}>
            <ErrorBoundary>
              <math {...expectMath}>
                <BrokenRender />
              </math>
            </ErrorBoundary>
          </foreignObject>
          <image {...expectSVG} />
        </svg>,
      );
      assertNamespacesMatch(<div {...expectHTML} />);
    });
    it('should unwind namespaces on caught errors in a portal', () => {
      function BrokenRender() {
        throw new Error('Hello');
      }
      class ErrorBoundary extends React.Component {