When setting boolean attributes on Web Components
`<x-search somebool name={this.props.name} />`
they get rendered as attribute/value pairs instead
`<x-search somebool="true" name={this.props.name}>`

This causes problems with some AMP components, for eg. `<amp-iframe />` which has a `resizable` attribute that gets rendered as `resizable="true"`. This results in non valid AMP content and developers crying with blood tears on their keyboards :)
> The attribute 'resizable' in tag 'amp-iframe' is set to the invalid value 'true'. (see https://www.ampproject.org/docs/reference/components/amp-iframe)

Is there any reason for the current behaviour? Will changing this break something else?
itRenders('cased custom attributes', async render => {
        const e = await render(<div fooBar="test" />, 1);
        expect(e.getAttribute('foobar')).toBe('test');
      });
    });
    itRenders('no HTML events', async render => {
      const e = await render(<div onClick={() => {}} />);
      expect(e.getAttribute('onClick')).toBe(null);
      expect(e.getAttribute('onClick')).toBe(null);
      expect(e.getAttribute('click')).toBe(null);
    });
    itRenders('no unknown events', async render => {
      const e = await render(<div onunknownevent='alert("hack")' />, 1);
      expect(e.getAttribute('onunknownevent')).toBe(null);
    });
    itRenders('custom attribute named `on`', async render => {
      const e = await render(<div on="tap:do-something" />);
      expect(e.getAttribute('on')).toEqual('tap:do-something');
    });
  });
  
  
  describe('custom elements', () => {
    itRenders('class for custom elements', async render => {
      const e = await render(<div is="custom-element" class="test" />, 0);
      expect(e.getAttribute('class')).toBe('test');
    });
    itRenders('className for custom elements', async render => {
      if (ReactFeatureFlags.enableCustomElementPropertySupport) {
        const e = await render(