For now, slice view shows screen title by default,
but it isn't approprate for some simple cases.
ie, device model, phone number, android version etc.
So, We create a new attribue which let BasePreferenceController
be more flxible. User can choose what they want to show
in summary text.
Fixes: 74900516
Test: make RunSettingsRoboTests
Change-Id: I2788c6edfaf8e656170a507607f22513841a3e0a
8eb46b717e