This allows app fragment use a less heavyweight fragment as super class
if they don't need PreferenceFragment. Using this class as base is
generally easier to set up robolectric tests too.
Bug: 33354536
Test: RunSettingsRoboTests
Change-Id: I91c4d242ea0333c76c8767c03c3f18dee6b6e104
Bug: 30681771
Test: SettingsUnitTests
Refactor visibility logging from InstrumentedFragment into a mixin. And
apply mixin in remaining fragments.
Change-Id: Ibbb59904336254a3e4bb9e8c7d0b36e5a6bc2622