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+<!--
+@license
+Copyright (C) 2019 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.
+-->
+
+<script>
+(function(window) {
+  'use strict';
+
+  window.Gerrit = window.Gerrit || {};
+
+  /** @polymerBehavior Gerrit.FireBehavior */
+  Gerrit.FireBehavior = {
+    /**
+     * Dispatches a custom event with an optional detail value.
+     *
+     * @param {string} type Name of event type.
+     * @param {*=} detail Detail value containing event-specific
+     *   payload.
+     * @param {{ bubbles: (boolean|undefined), cancelable: (boolean|undefined),
+     *     composed: (boolean|undefined) }=}
+     *  options Object specifying options.  These may include:
+     *  `bubbles` (boolean, defaults to `true`),
+     *  `cancelable` (boolean, defaults to false), and
+     *  `composed` (boolean, defaults to true).
+     * @return {!Event} The new event that was fired.
+     * @override
+     */
+    fire(type, detail, options) {
+      options = options || {};
+      detail = (detail === null || detail === undefined) ? {} : detail;
+      const event = new Event(type, {
+        bubbles: options.bubbles === undefined ? true : options.bubbles,
+        cancelable: Boolean(options.cancelable),
+        composed: options.composed === undefined ? true: options.composed,
+      });
+      event.detail = detail;
+      this.dispatchEvent(event);
+      return event;
+    },
+  };
+})(window);
+</script>