Add the ability to refresh to the captive portal app.

Bug: 69840796
Test: manual
      created a small app that brings up the captive portal app,
      checked that pulling down does show the refresh spinner,
      refresh the page, and hide the spinner when refreshed.
      Checked that it works multiple times in a row.

Change-Id: Ieefdaffa9325b0c5f1b02ab6052c29a381f3a4d4