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diff --git a/browser/components/syncedtabs/EventEmitter.jsm b/browser/components/syncedtabs/EventEmitter.jsm
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+this.EXPORTED_SYMBOLS = [
+ "EventEmitter"
+];
+
+// Simple event emitter abstraction for storage objects to use.
+function EventEmitter () {
+ this._events = new Map();
+}
+
+EventEmitter.prototype = {
+ on(event, listener) {
+ if (this._events.has(event)) {
+ this._events.get(event).add(listener);
+ } else {
+ this._events.set(event, new Set([listener]));
+ }
+ },
+ off(event, listener) {
+ if (!this._events.has(event)) {
+ return;
+ }
+ this._events.get(event).delete(listener);
+ },
+ emit(event, ...args) {
+ if (!this._events.has(event)) {
+ return;
+ }
+ for (let listener of this._events.get(event).values()) {
+ try {
+ listener.apply(this, args);
+ } catch (e) {
+ Cu.reportError(e);
+ }
+ }
+ },
+};
+