d26449fd76
Periodically records delta network traffic into historical buckets to support other services, such NetworkPolicyManager and Settings UI. Introduces NetworkStatsHistory structure which contains sparse, uniform buckets of data usage defined by timestamps. Service periodically polls NetworkStats and records changes into buckets. It only persists to disk when substantial changes have occured. Current parameters create 4 buckets each day, and persist for 90 days, resulting in about 8kB of data per network. Only records stats for "well known" network interfaces that have been claimed by Telephony or Wi-Fi subsystems. Historical stats are also keyed off identity (such as IMSI) to support SIM swapping. Change-Id: Ia27d1289556a2bf9545fbc4f3b789425a01be53a