getChildContext () {
    return {}
  }
Provides the context which is delivered to every child component. Override
    if you want to provide your own child context. Child context is available to
    all components rendered from within this component's render method as
    `this.context`.

    @example

    ```
    class A extends Component {
    ...
      getChildContext() {
        // Optional, but useful to merge super's context
        return Object.assign({}, super.getChildContext(), {foo: 'bar'})
      }

      render($$) {
        return $$(B)
      }
    }

    class B extends Component {
      render($$) {
        // this.context.foo is available here
      }
    }
    ```
    Component

    @return {Object} the child context