When navigating away from a preferences screen and unsaved settings would be
lost, display a confirmation dialog. The user can either accept or cancel the
action. If canceling, the user is returned to the settings screen they were
currently on. Otherwise, they are taken to a new fragment (the exact
destination depends upon whether the user navigated "back" or selected another
header)
There is one additional change that needs to be made. In the case of navigating
to another header, we are notified _after_ the new header is selected. In this
scenario, the action is not cancelable and the user will lose any changes. We
must display an appropriate message when this happens. [note: this is the same
behaviour as when the user selects a breadcrumb]
bug 3327737
Change-Id: I4bd3b393a6323f3e63510e3ed08e4e1e745b04c4
c890a4e4a2