Misc memory stuff.

- New Activity.reportFullyDrawn() method that applicatins can call
  when they know they are fully drawn, allowing us to have better
  app launch time info.  This data is also included in usage stats.
- Added total and free memory data "dumpsys meminfo".
- Tuned the moderate memory levels to be more aggressive about
  considering the device getting low on RAM, and thus starting
  to prune RAM from processes.
- Fixed issues in processstats when reading old data as well as
  resetting and other various fixes.

Change-Id: I20efe7451afb4edfa1aeec448328ba601c24d869