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/AbstractMetric.java

@@ -0,0 +1,60 @@
+// 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 com.google.common.base.MoreObjects;
+import com.google.common.collect.ImmutableSet;
+import google.registry.monitoring.metrics.MetricSchema.Kind;
+
+//TODO(shikhman): implement HistogramMetrics.
+abstract class AbstractMetric<V> implements Metric<V> {
+
+  private final Class<V> valueClass;
+  private final MetricSchema metricSchema;
+
+  AbstractMetric(
+      String name,
+      String description,
+      String valueDisplayName,
+      Kind kind,
+      ImmutableSet<LabelDescriptor> labels,
+      Class<V> valueClass) {
+    this.metricSchema = MetricSchema.create(name, description, valueDisplayName, kind, labels);
+    this.valueClass = valueClass;
+  }
+
+  /** Returns the schema of this metric. */
+  @Override
+  public final MetricSchema getMetricSchema() {
+    return metricSchema;
+  }
+
+  /**
+   * Returns the type for the value of this metric, which would otherwise be erased at compile-time.
+   * This is useful for implementors of {@link MetricWriter}.
+   */
+  @Override
+  public final Class<V> getValueClass() {
+    return valueClass;
+  }
+
+  @Override
+  public final String toString() {
+    return MoreObjects.toStringHelper(this)
+        .add("valueClass", valueClass)
+        .add("schema", metricSchema)
+        .toString();
+  }
+}