Indexing in DataUsage was not conventional, since it
blocked adding XML based on current sim status rather than
indexing everything and changing non-indexabe keys.
Manual merge for: ag/2631595
Change-Id: I7bb3cdb0f11772bbaefb6c21c61eb63bd0b17c7e
Fixes: 64193449
Test: robotests
Move public static methods from DataUsageSummary to DataUsageBase.
Bug: 62349208
Test: make RunSettingsRoboTests -j40
Change-Id: I632f75f4c4f370fb225a9787267043fec20994e5