MD Settings: Creating WebUIListenerBehavior helper.

chrome/browser/resources/settings/web_ui_listener_behavior.js

Index: chrome/browser/resources/settings/web_ui_listener_behavior.js
diff --git a/chrome/browser/resources/settings/web_ui_listener_behavior.js b/chrome/browser/resources/settings/web_ui_listener_behavior.js
new file mode 100644
index 0000000000000000000000000000000000000000..b3c44cdafe4f8c9f5262d9b631fe9837b8c99a0d
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+++ b/chrome/browser/resources/settings/web_ui_listener_behavior.js
@@ -0,0 +1,52 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview Behavior to be used by Polymer elements that want to
+ * automatically remove WebUI listeners when detached.
+ *
+ * TODO(dpapad): This file can be useful for any WebUI Polymer code, not just
+ * for settings, consider moving elsewhere.
+ */
+
+cr.define('settings', function() {
+  /** @polymerBehavior */
+  var WebUIListenerBehavior = {
+    properties: {
+      /**
+       * Holds WebUI listeners that need to be removed when this element is
+       * destroyed.
+       * @private {!Array<!WebUIListener>}
+       */
+      webUIListeners_: {
+        type: Array,
+        value: function() { return []; },
+      },
+    },
+
+    /**
+     * Adds a WebUI listener and registers it for automatic removal when this
+     * element is detached.
+     * Note: Do not use this method if you intend to remove this listener
+     * manually (use cr.addWebUIListener directly instead).
+     *
+     * @param {string} eventName The event to listen to.
+     * @param {!Function} callback The callback run when the event is fired.
+     */
+    addWebUIListener: function(eventName, callback) {
+      this.webUIListeners_.push(cr.addWebUIListener(eventName, callback));
+    },
+
+    /** @override */
+    detached: function() {

[Dan Beam, 2016/02/23 02:38:28]

it may make more sense for this to be named removeAllListeners and for those
this behavior to call from detached()

this is OK for now

[Dan Beam, 2016/02/23 02:51:07]

for those that want this behavior*

+      while (this.webUIListeners_.length > 0) {
+        cr.removeWebUIListener(this.webUIListeners_.pop());
+      }
+    },
+  };
+
+  return {
+    WebUIListenerBehavior: WebUIListenerBehavior,
+  };
+});