Refactor EppMetrics into the EppMetric value type

This change refactors EppMetrics from the mutable self-exporting thing that it
was into a real value type EppMetric, and delegates exporting functionality to the
BigQueryMetricsEnqueuer.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132387660

java/google/registry/monitoring/whitebox/BigQueryMetricsEnqueuer.java

@@ -0,0 +1,69 @@
+// 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.monitoring.whitebox;
+
+import static com.google.appengine.api.taskqueue.QueueFactory.getQueue;
+import static com.google.appengine.api.taskqueue.TaskOptions.Builder.withUrl;
+
+import com.google.appengine.api.modules.ModulesService;
+import com.google.appengine.api.taskqueue.TaskOptions;
+import com.google.appengine.api.taskqueue.TransientFailureException;
+import com.google.common.annotations.VisibleForTesting;
+import google.registry.util.FormattingLogger;
+import java.util.Map.Entry;
+import java.util.UUID;
+import javax.inject.Inject;
+
+/**
+ * A collector of metric information. Enqueues collected metrics to a task queue to be written to
+ * BigQuery asynchronously.
+ *
+ * @see MetricsExportAction
+ */
+public class BigQueryMetricsEnqueuer {
+
+  private static final FormattingLogger logger = FormattingLogger.getLoggerForCallerClass();
+
+  public static final String QUEUE = "bigquery-streaming-metrics";
+
+  @Inject ModulesService modulesService;
+
+  @Inject
+  BigQueryMetricsEnqueuer() {}
+
+  @VisibleForTesting
+  void export(BigQueryMetric metric, String insertId) {
+    try {
+      String hostname = modulesService.getVersionHostname("backend", null);
+      TaskOptions opts =
+          withUrl(MetricsExportAction.PATH)
+              .header("Host", hostname)
+              .param("insertId", insertId);
+      for (Entry<String, String> entry : metric.getBigQueryRowEncoding().entrySet()) {
+        opts.param(entry.getKey(), entry.getValue());
+      }
+      opts.param("tableId", metric.getTableId());
+      getQueue(QUEUE).add(opts);
+    } catch (TransientFailureException e) {
+      // Log and swallow. We may drop some metrics here but this should be rare.
+      logger.info(e, e.getMessage());
+    }
+  }
+
+  /** Enqueue a metric to be exported to BigQuery. */
+  public void export(BigQueryMetric metric) {
+    export(metric, UUID.randomUUID().toString());
+  }
+}