Record process start time for native processes

Process start time is recorded to detect whether two memory samples
come from the same process and how long the process was alive.

Bug: 118249210
Test: atest MemoryStatUtilTest and manually verified that data is in
statsd report

Change-Id: I7f49cd8bfc81c5e7e70e4f8b49729632eeec5798
1 file changed
tree: eb62cccd8f3b11ac68b9b297ea28164c0b316a58
  1. atom_field_options.proto
  2. atoms.proto