We need to eagerly load the performance bar wrapper component
(`performance_bar/index.js`) when the page is loaded and the container element
is present, to ensure that we register the interceptor early enough in the
page's lifecycle.
However, we don't need to load the UI at that point. Not doing so means that we
can let Webpack extract the UI (`performance_bar/components/*`) into its own
chunk, so users who don't see the performance bar don't have to load too much
unnecessary JavaScript.
