For ajax callbacks that want to inform Drupal about something related to the current page, there is not guaranteed way to find the current page path.
We already add the base path and other info to the JS settings, we should add the Drupal path of the current page too.
Note by default this and more info is exposed in the CSS classes in the HTML, but reconstructing the path from that is going to be fragile so it would be better to have a guaranteed place to find it.
PASSED: [[SimpleTest]]: [MySQL] 57,899 pass(es). View
PASSED: [[SimpleTest]]: [MySQL] 57,973 pass(es). View