Update summary correctly in Settings dashboard.

Bug: 30490325

SummaryLoader needs DashboardCategory to update summary and it currently
ask for it from DashboardAdapter. But DashboardCategory is not always
available in DashboardAdapter. When SummaryLoader wants to get category
from adapter before adapter is ready, it won't have it, causing summary
to appear blank sometimes.

The fix is to get category from data source directly.

Change-Id: I9d7f676954d1cece42d6e03748ab7aa35357f8b7