Change toolbar button to mw-ui-progressive.

* mw-ui-primary is deprecated.
* mw-ui-progressive is semantically correct since it starts a flow
  rather than finishing a process (i.e. click and done).
* Coincidentally, this looks the same as primary.

Change-Id: I4d484fe297a316a34e5250986356964b3d3a33d8
Merge "Change toolbar button to mw-ui-progressive."