UNREVIEWED: TAPL prototype for in-lab flake test

These sources didn't pass a normal CR, and mustn't be used in prod. The
goal of landing them is to start in-lab flakiness tests ASAP. A normal
code review will follow after landing cleanup CLs.

Bug: 110103162
Test: Running TaplTests suite
Change-Id: I051591c9af7822d4cbae4261e66563f1ccc1cfcc