Tests Accessibility.getChildAXNodes

After getFullAXTree:
RootWebArea
  main
    article
    Iframe

After getChildAXNodes:
RootWebArea
  main
    article
      heading "Article"
      paragraph
    Iframe

getChildAXNodes iframe:
RootWebArea
  main
    article
      heading "Article"
      paragraph
    Iframe
      RootWebArea "Iframe with accessible name"
        heading "accessible name"