SaveOnChangePage force dirty saving on navigation.

[#60875594]
https://www.pivotaltracker.com/story/show/60875594
(cherry picked from commit 8e7d097a57fd00fa13871082018e9026e7bb8981)
Jasmine test for SaveOnChangePage force dirty saving on navigation.

Also:  Add ajax_matching helper to reduce boilerplate test noise.

[#60875594]
https://www.pivotaltracker.com/story/show/60875594
(cherry picked from commit 8e887fbdd18bc66f505d41a8b37b2506fae89971)