[#735] policer: Allow to provide metrics from the outside

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/services/policer/metrics.go

@@ -3,3 +3,7 @@ package policer
 type MetricsRegister interface {
 	IncProcessedObjects()
 }
+
+type noopMetrics struct{}
+
+func (noopMetrics) IncProcessedObjects() {}

pkg/services/policer/option.go

@@ -81,6 +81,7 @@ func defaultCfg() *cfg {
 		rebalanceFreq: 1 * time.Second,
 		sleepDuration: 1 * time.Second,
 		evictDuration: 30 * time.Second,
+		metrics:       noopMetrics{},
 	}
 }
 
@@ -172,3 +173,10 @@ func WithPool(p *ants.Pool) Option {
 		c.taskPool = p
 	}
 }
+
+// WithMetrics returns option to set metrics.
+func WithMetrics(m MetricsRegister) Option {
+	return func(c *cfg) {
+		c.metrics = m
+	}
+}