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diff --git a/java/com/google/gerrit/metrics/Histogram3.java b/java/com/google/gerrit/metrics/Histogram3.java
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+++ b/java/com/google/gerrit/metrics/Histogram3.java
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+// Copyright (C) 2015 The Android Open Source Project
+//
+// 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 com.google.gerrit.metrics;
+
+import com.google.gerrit.extensions.registration.RegistrationHandle;
+
+/**
+ * Measures the statistical distribution of values in a stream of data.
+ *
+ * <p>Suitable uses are "response size in bytes", etc.
+ *
+ * @param <F1> type of the field.
+ * @param <F2> type of the field.
+ * @param <F3> type of the field.
+ */
+public abstract class Histogram3<F1, F2, F3> implements RegistrationHandle {
+  /**
+   * Record a sample of a specified amount.
+   *
+   * @param field1 bucket to record sample
+   * @param field2 bucket to record sample
+   * @param field3 bucket to record sample
+   * @param value value to record
+   */
+  public abstract void record(F1 field1, F2 field2, F3 field3, long value);
+}