Add metrics for on-device signing

These metrics are generated when a new ART APEX is installed or a
device takes an OTA. They give insights into whether AOT compilation
of the boot classpath and system_server succeeded, how long it took,
and what the storage overhead was.

Bug: 169925964
Test: manual
Change-Id: I7f670eda2699c890d3340964747945c5bd2bf708
1 file changed
tree: da440a430f824c0ba88da42d9d34c4ceef2a4ad9
  1. stats/
  2. OWNERS