ContactsProvider2 optimization: caching raw contact IDs involved in aggregation exceptions

This saves one query per contact.

Number or object per contact (~1700) and time per contact (~125ms on Sholes) 
does not seem to be significantly affected by this optimization.  
Should probably submit this anyway and see its effect on really 
large accounts (e.g. 5000 contacts)

Bug: http://b/2148645

Change-Id: I57457201017463e519ed55dddda75a0d802f0d9a
2 files changed