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
Unless a fragment is grandfathered:
- If it's a SearchPreferenceFragment, it needs to implement Indexable.
- If it's a Indexable, it needs to contain SEARCH_INDEX_DATA_PROVIDER.
Bug: 33209410
Test: make RunSettingsRoboTests
Change-Id: I078c54374341ba2966145429fc1507a3d5763d3b