Enable Systrace to be used during boot.

- Add BootAgent, which is an AtraceAgent specializing in tracing
  the boot sequence, and its test.
- Add --boot option. This sets persist.debug.atrace.boottrace
  property, which triggers atrace during boot, writes categories
  to /data/local/tmp/boottracecategories, which is used by atrace
  as enabled categories, and reboots the device. Once the device
  has booted up, the report is created by the user hitting

BUG: 21739901
Change-Id: I5e27a402f3d32cb151227d3d222c05da39eca28c
3 files changed