Make lists in the passwords section aware of the scroll target.

chrome/browser/resources/settings/global_scroll_target_behavior.js

+// 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 A helper object to be used when an iron-list needs to be aware
+ * of a global scroll target.

[michaelpg, 2016/10/19 19:50:09]

I'd add a little more instruction here, e.g. that the effect is elements w/ this
behavior get a |scrollTarget| property which is set just after initialization.

[hcarmona, 2016/10/20 14:27:44]

Done.

+ */
+
+/**
+ * Global object to hold the scroll target.
+ * @type {{
+ *   targetPromise: (Promise<HTMLElement>|undefined),
+ *   fulfillPromise: (function(HTMLElement)|undefined),
+ * }}
+ */
+global.settingsScrollTargetData = {};

[michaelpg, 2016/10/19 19:50:09]

where does |global| actually come from? dunno why we use both global and window
for the same thing.

[hcarmona, 2016/10/20 14:27:44]

|global| is defined here:
https://cs.chromium.org/chromium/src/ui/webui/resources/js/cr.js?rcl=0&l=10

No longer global, since wrapped in a function.

+/** @type {Promise<HTMLElement>} */
+global.settingsScrollTargetData.targetPromise = new Promise(function(accept) {

[michaelpg, 2016/10/19 19:50:09]

Would our PromiseResolver be more convenient?

[hcarmona, 2016/10/20 14:27:44]

Yes

+  global.settingsScrollTargetData.fulfillPromise = accept;
+});
+
+/** @polymerBehavior */
+var GlobalScrollTargetBehavior = {
+  properties: {
+    /**
+     * Read only property for the scroll target.
+     * @type {HTMLElement}
+     */
+    scrollTarget: {
+      type: Object,
+      notify: true,

[michaelpg, 2016/10/19 19:50:09]

Shouldn't need notify: true; as we're not 2-way binding (setting passwords
section's scrollTarget shouldn't propagate *up* to settings-ui)

[hcarmona, 2016/10/20 14:27:44]

Done.

+      readOnly: true,
+    },
+  },
+
+  /**
+   * Reference to the global data. This allows Polymer style data binding.

[michaelpg, 2016/10/19 19:50:08]

comment outdated

[hcarmona, 2016/10/20 14:27:44]

Acknowledged.

+   * @type {{
+   *   targetPromise: (Promise<HTMLElement>|undefined),

[michaelpg, 2016/10/19 19:50:09]

make a typedef instead of copying/pasting

[hcarmona, 2016/10/20 14:27:44]

Acknowledged.

+   *   fulfillPromise: (function(HTMLElement)|undefined),
+   * }}
+   * @private
+   */
+  globalData_: global.settingsScrollTargetData,
+
+  /** @override */
+  attached: function() {
+    this.globalData_.targetPromise.then(function(scrollTarget) {
+      this._setScrollTarget(scrollTarget);
+    }.bind(this));
+  },
+
+  /**
+   * This should only be called once.
+   * @param {HTMLElement} value
+   */
+  setGlobalScrollTarget: function(value) {
+    this.globalData_.fulfillPromise(value);
+  },
+};