Reactor-based alarm implementation

* Use Reactor+Thread (common/thread.h) to replace existing
  libchrome-based message_loop_thread
* Use Alarm/RepeatingAlarm to replace existing Timer, by using
  kernel-based timerfd, to make all components unified

Bug: 110303473
Test: run unit test, and run benchmark
Change-Id: I6d6bc8dc3897649d0f6cc00ce0aa7054a3ddc09d