Add metrics for the new Check API

New metrics are necessary because the new API no longer wraps
an EPP flow, therefore does not get metrics for free.

Metrics include
 - An EventMetric for processing time
 - An IncrementableMetric for request count, with
   availability (available/reserved/registered) and
   pricing (standard/premium) fields

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=199708592

java/google/registry/monitoring/whitebox/CheckApiMetric.java

@@ -0,0 +1,124 @@
+// Copyright 2018 The Nomulus 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.common.base.Preconditions.checkNotNull;
+
+import com.google.auto.value.AutoValue;
+import google.registry.util.Clock;
+import java.util.Optional;
+import org.joda.time.DateTime;
+
+/** A value class for recording attributes of a domain check metric. */
+@AutoValue
+public abstract class CheckApiMetric {
+
+  /** Price tier of a domain name. */
+  public enum Tier {
+    STANDARD("standard"),
+    PREMINUM("premium");
+
+    private final String displayLabel;
+
+    private Tier(String displayLabel) {
+      this.displayLabel = displayLabel;
+    }
+
+    public String getDisplayLabel() {
+      return displayLabel;
+    }
+  }
+
+  /** Availability status of a domain. */
+  public enum Availability {
+    RESERVED("reserved"),
+    REGISTERED("registered"),
+    AVAILABLE("available");
+
+    private final String displayLabel;
+
+    private Availability(String displayLabel) {
+      this.displayLabel = displayLabel;
+    }
+
+    public String getDisplayLabel() {
+      return displayLabel;
+    }
+  }
+
+  /** Status of the CheckApi command. */
+  public enum Status {
+    SUCCESS("success"),
+    INVALID_NAME("invalid_name"),
+    INVALID_REGISTRY_PHASE("invalid_registry_phase"),
+    UNKNOWN_ERROR("unknown_error");
+
+    private final String displayLabel;
+
+    private Status(String displayLabel) {
+      this.displayLabel = displayLabel;
+    }
+
+    public String getDisplayLabel() {
+      return displayLabel;
+    }
+  }
+
+  public abstract DateTime startTimestamp();
+
+  public abstract DateTime endTimestamp();
+
+  public abstract Status status();
+
+  public abstract Optional<Tier> tier();
+
+  public abstract Optional<Availability> availability();
+
+  public static Builder builder(Clock clock) {
+    return new AutoValue_CheckApiMetric.Builder().startTimestamp(clock.nowUtc()).setClock(clock);
+  }
+
+  CheckApiMetric() {}
+
+  /** Builder for {@link CheckApiMetric}. */
+  @AutoValue.Builder
+  public abstract static class Builder {
+
+    private Clock clock;
+
+    /** Saves the {@link Clock} for end-time determination. */
+    Builder setClock(Clock clock) {
+      checkNotNull(clock, "clock");
+      this.clock = clock;
+      return this;
+    }
+
+    public CheckApiMetric build() {
+      return this.endTimestamp(clock.nowUtc()).autoBuild();
+    }
+
+    abstract Builder startTimestamp(DateTime startTimestamp);
+
+    abstract Builder endTimestamp(DateTime endTimestamp);
+
+    public abstract Builder status(Status status);
+
+    public abstract Builder tier(Tier tier);
+
+    public abstract Builder availability(Availability availability);
+
+    abstract CheckApiMetric autoBuild();
+  }
+}