This makes the constructor and the unchecked create functions
constexpr on the unit classes Timestamp, TimeDelta, Datarate and
DataSize. This allows using the units in constexpr constants.
Unchecked access methods are made constexpr as well. Making them
usable in static asserts.
Constexpr create functions for checked construction is added in
a separate CL.
Bug: webrtc:9574
Change-Id: I605ae2e8572195dbb2078c283056208be0f43333
Reviewed-on: https://webrtc-review.googlesource.com/91160
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24206}
8e06419ee9