Merge branch 'master' into stable-3.5

* master:
  TaskTree: remove 'ERROR:' prefix from log statement
  TaskTree: fix errorprone warning about Flogger

Most development has happened in the stable-3.5 branch, but master has a
couple commits missing from there. Merge them in before creating new
stable branches based on stable-3.5.

Change-Id: I0698db5f5cdadb5b208fdac09e0a4ffece20b2d0