Initial step of unifying so that base/timeutils.h and Clock/TimeTime from system_wrappers use the same implementation. BUG=webrtc:5463 R=pbos@webrtc.org, tommi@webrtc.org Review URL: https://codereview.webrtc.org/1639543005 . Cr-Commit-Position: refs/heads/master@{#11394}