Make LatencyInfo to be class

LatencyInfo has grown to be more than a pure data holder
struct. Make it a class so that we have a clean API
surface that can access/modify the data members.

BUG=None
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1245753003

Cr-Commit-Position: refs/heads/master@{#341831}
41 files changed