Merge changes Ic7620978,I6d5bab58,Id1668c26,Icdb56b6f,Ic0c86a2b

* changes:
  logd: remove FlushCommand
  logd: rename mOldest -> oldest_
  logd: separate PruneList from LogBuffer
  logd: don't use SIGHUP to reinitialize
  logd: decouple LogTags from LogBuffer