Refactor client-go/util/flowcontrol/throttle.go RateLimiter

- Introduce PassiveRateLimiter which implements all methods of previous RateLimiter except Accept() and Wait()
- Change RateLimiter interface to extend PassiveRateLimiter by additionally implementing Accept() and Wait()
- Make client-go/tools/record use PassiveRateLimiter

Refactor EventSourceObjectSpamFilter, EventAggregator, EventCorrelator

- EventSourceObjectSpamFilter, EventAggregator, EventCorrelator use clock.PassiveClock now.
	- This won't be a breaking change because even if a clock.Clock is passed, it still implements the clock.PassiveClock interface.
- Extend clock.PassiveClock through Clock.
- Replace pacakge local implementation of realClock with clock.RealClock
- In flowcontrol/throttle.go split tokenBucketRateLimiters to use Clock and clock.PassiveClock.
- Migrate client-go/tools/record tests from using IntervalClock to using SimpleIntervalClock (honest implementation of clock.PassiveClock)

Signed-off-by: Madhav Jivrajani <madhav.jiv@gmail.com>

Kubernetes-commit: ac5c55f0bd853fcf883d9b8e1f5ef728a2fb5309

tools/record/event.go

@@ -81,7 +81,7 @@ type CorrelatorOptions struct {
 	MaxIntervalInSeconds int
 	// The clock used by the EventAggregator to allow for testing
 	// If not specified (zero value), clock.RealClock{} will be used
-	Clock clock.Clock
+	Clock clock.PassiveClock
 	// The func used by EventFilterFunc, which returns a key for given event, based on which filtering will take place
 	// If not specified (zero value), getSpamKey will be used
 	SpamKeyFunc EventSpamKeyFunc
@@ -323,7 +323,7 @@ type recorderImpl struct {
 	scheme *runtime.Scheme
 	source v1.EventSource
 	*watch.Broadcaster
-	clock clock.Clock
+	clock clock.PassiveClock
 }
 
 func (recorder *recorderImpl) generateEvent(object runtime.Object, annotations map[string]string, eventtype, reason, message string) {