Add StackDriver implementation, in monitoring/metrics package

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=130287319

java/google/registry/monitoring/metrics/MetricPoint.java

@@ -0,0 +1,54 @@
+// 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.metrics;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import org.joda.time.Instant;
+
+/**
+ * Value type class to store a point-in-time snapshot of a {@link Metric} value for a given label
+ * value tuple.
+ */
+@AutoValue
+public abstract class MetricPoint<V> {
+
+  private static final String LABEL_COUNT_ERROR =
+      "The count of labelsValues must be equal to the underlying "
+          + "MetricDescriptor's count of labels.";
+
+  MetricPoint() {}
+
+  /**
+   * Returns a new {@link MetricPoint}. Callers should insure that the count of {@code labelValues}
+   * matches the count of labels for the given metric.
+   */
+  static <V> MetricPoint<V> create(
+      Metric<V> metric, ImmutableList<String> labelValues, Instant timestamp, V value) {
+    checkArgument(
+        labelValues.size() == metric.getMetricSchema().labels().size(), LABEL_COUNT_ERROR);
+    return new AutoValue_MetricPoint<>(metric, labelValues, timestamp, value);
+  }
+
+  public abstract Metric<V> metric();
+
+  public abstract ImmutableList<String> labelValues();
+
+  public abstract Instant timestamp();
+
+  public abstract V value();
+}