Merge "bootstat: Calculate and log the time_since_last_boot metric." am: 1607ea6
am: db20ad1

* commit 'db20ad1222661f3e486a19791476ce0189cdfcac':
  bootstat: Calculate and log the time_since_last_boot metric.

Change-Id: I11f52f086adf2faa363f681534566943f2252f00