Add metrics to PublishDnsUpdatesAction

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=131190862

java/google/registry/module/backend/BackendComponent.java

@@ -47,6 +47,7 @@ import javax.inject.Singleton;
 @Component(
     modules = {
         AppIdentityCredentialModule.class,
+        BackendMetricsModule.class,
         BigqueryModule.class,
         ConfigModule.class,
         DatastoreServiceModule.class,

java/google/registry/module/backend/BackendMetricsModule.java

@@ -0,0 +1,34 @@
+// Copyright 2016 The Domain Registry Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.module.backend;
+
+import dagger.Module;
+import dagger.Provides;
+import google.registry.dns.DnsMetrics;
+import javax.inject.Singleton;
+
+/**
+ * Dagger module for injecting metrics. All metrics should have {@link Singleton} scope to avoid
+ * being recreated per-request, as the metrics generally track cumulative values.
+ */
+@Module
+public class BackendMetricsModule {
+
+  @Provides
+  @Singleton
+  static DnsMetrics provideDnsMetrics() {
+    return new DnsMetrics();
+  }
+}