ReplicationMetrics: Make members private final

These members should only be accessed through the public methods:

 - start(...), to create/start a new timer context
 - record(...), to record the retry/delay values

Mark the members as private final to prevent unintended access.

Change-Id: I69a7e3b13ba4c344f3176528306163ebef07653c

src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationMetrics.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationMetrics.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationMetrics.java
index e02084d..a7b27a0 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationMetrics.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationMetrics.java
@@ -24,9 +24,9 @@
 
 @Singleton
 public class ReplicationMetrics {
-  Timer1<String> executionTime;
-  Histogram1<String> executionDelay;
-  Histogram1<String> executionRetries;
+  private final Timer1<String> executionTime;
+  private final Histogram1<String> executionDelay;
+  private final Histogram1<String> executionRetries;
 
   @Inject
   ReplicationMetrics(MetricMaker metricMaker) {