Replace anonymous classes with lambdas

Change-Id: Ia50a1a6a8f7de93941702878b9b9966a565deec8

java/com/google/gerrit/metrics/dropwizard/CallbackMetricImpl0.java

@@ -14,6 +14,7 @@
 
 package com.google.gerrit.metrics.dropwizard;
 
+import com.codahale.metrics.Gauge;
 import com.codahale.metrics.MetricRegistry;
 import com.google.gerrit.metrics.CallbackMetric0;
 
@@ -71,12 +72,10 @@ class CallbackMetricImpl0<V> extends CallbackMetric0<V> implements CallbackMetri
   public void register(Runnable trigger) {
     registry.register(
         name,
-        new com.codahale.metrics.Gauge<V>() {
-          @Override
-          public V getValue() {
-            trigger.run();
-            return value;
-          }
-        });
+        (Gauge<V>)
+            () -> {
+              trigger.run();
+              return value;
+            });
   }
 }

java/com/google/gerrit/metrics/dropwizard/DropWizardMetricMaker.java

@@ -305,14 +305,7 @@ public class DropWizardMetricMaker extends MetricMaker {
     }
     trigger.run();
 
-    return new RegistrationHandle() {
-      @Override
-      public void remove() {
-        for (CallbackMetricGlue m : all) {
-          m.remove();
-        }
-      }
-    };
+    return () -> all.forEach(CallbackMetricGlue::remove);
   }
 
   synchronized void remove(String name) {