Move all Clock methods except Now to new interface SampledClock.
Move SampledTimer's exported methods (except SetClock) to new interface
Timer. Combine Swap and SwapAnd into Set to reduce the number of redundant
methods that must be implemented.
Add interface method Clock.NewTimer.
This is in preparation for cl/693856539, which adds a second Timer
implementation.
ktime: support varying Timer implementations
Rename Timer to SampledTimer.
Move all Clock methods except Now to new interface SampledClock.
Move SampledTimer's exported methods (except SetClock) to new interface Timer. Combine Swap and SwapAnd into Set to reduce the number of redundant methods that must be implemented.
Add interface method Clock.NewTimer.
This is in preparation for cl/693856539, which adds a second Timer implementation.