Add TUIC protocol

transport/tuic/congestion/clock.go

@@ -0,0 +1,20 @@
+package congestion
+
+import "time"
+
+// A Clock returns the current time
+type Clock interface {
+	Now() time.Time
+}
+
+// DefaultClock implements the Clock interface using the Go stdlib clock.
+type DefaultClock struct {
+	TimeFunc func() time.Time
+}
+
+var _ Clock = DefaultClock{}
+
+// Now gets the current time
+func (c DefaultClock) Now() time.Time {
+	return c.TimeFunc()
+}