func (s systemTimeSource) Now() time.Time {
	return time.Now()
}
Now returns the true current local time.
package clock
import (
	"sync"
	"time"
	"github.com/golang/glog"
)
var System TimeSource = systemTimeSource{}
type TimeSource interface {
	Now() time.Time
	NewTimer(d time.Duration) Timer
}
func SecondsSince(ts TimeSource, t time.Time) float64 {
	return ts.Now().Sub(t).Seconds()
}
type systemTimeSource struct{}