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diff --git a/tools/addon-sdk-1.7/packages/api-utils/lib/tabs/observer.js b/tools/addon-sdk-1.7/packages/api-utils/lib/tabs/observer.js
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@@ -0,0 +1,93 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/* 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 { EventEmitterTrait: EventEmitter } = require("../events");
+const { DOMEventAssembler } = require("../events/assembler");
+const { Trait } = require("../light-traits");
+const { getActiveTab, getTabs, getTabContainers } = require("./utils");
+const { browserWindowIterator, isBrowser } = require("../window-utils");
+const { observer: windowObserver } = require("../windows/observer");
+
+const EVENTS = {
+  "TabOpen": "open",
+  "TabClose": "close",
+  "TabSelect": "select",
+  "TabMove": "move",
+  "TabPinned": "pinned",
+  "TabUnpinned": "unpinned"
+};
+
+
+// Event emitter objects used to register listeners and emit events on them
+// when they occur.
+const observer = Trait.compose(DOMEventAssembler, EventEmitter).create({
+  /**
+   * Method is implemented by `EventEmitter` and is used just for emitting
+   * events on registered listeners.
+   */
+  _emit: Trait.required,
+  /**
+   * Events that are supported and emitted by the module.
+   */
+  supportedEventsTypes: Object.keys(EVENTS),
+  /**
+   * Function handles all the supported events on all the windows that are
+   * observed. Method is used to proxy events to the listeners registered on
+   * this event emitter.
+   * @param {Event} event
+   *    Keyboard event being emitted.
+   */
+  handleEvent: function handleEvent(event) {
+    this._emit(EVENTS[event.type], event.target, event);
+  }
+});
+
+// Currently gecko does not dispatches any event on the previously selected
+// tab before / after "TabSelect" is dispatched. In order to work around this
+// limitation we keep track of selected tab and emit "deactivate" event with
+// that before emitting "activate" on selected tab.
+var selectedTab = null;
+function onTabSelect(tab) {
+  if (selectedTab !== tab) {
+    if (selectedTab) observer._emit("deactivate", selectedTab);
+    if (tab) observer._emit("activate", selectedTab = tab);
+  }
+};
+observer.on("select", onTabSelect);
+
+// We also observe opening / closing windows in order to add / remove it's
+// containers to the observed list.
+function onWindowOpen(chromeWindow) {
+  if (!isBrowser(chromeWindow)) return; // Ignore if it's not a browser window.
+  getTabContainers(chromeWindow).forEach(function (container) {
+    observer.observe(container);
+  });
+}
+windowObserver.on("open", onWindowOpen);
+
+function onWindowClose(chromeWindow) {
+  if (!isBrowser(chromeWindow)) return; // Ignore if it's not a browser window.
+  getTabContainers(chromeWindow).forEach(function (container) {
+    observer.ignore(container);
+  });
+}
+windowObserver.on("close", onWindowClose);
+
+
+// Currently gecko does not dispatches "TabSelect" events when different
+// window gets activated. To work around this limitation we emulate "select"
+// event for this case.
+windowObserver.on("activate", function onWindowActivate(chromeWindow) {
+  if (!isBrowser(chromeWindow)) return; // Ignore if it's not a browser window.
+  observer._emit("select", getActiveTab(chromeWindow));
+});
+
+// We should synchronize state, since probably we already have at least one
+// window open.
+for each (let window in browserWindowIterator()) onWindowOpen(window);
+
+exports.observer = observer;