MD Settings: make the background color of the collapsed nav drawer white

chrome/browser/resources/settings/settings_ui/settings_ui.js

 // Copyright 2015 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
  * 'settings-ui' implements the UI for the Settings page.
  *
  * Example:
  *
  *    <settings-ui prefs="{{prefs}}"></settings-ui>
  */
 Polymer({
   is: 'settings-ui',
 
   properties: {
     /**
      * Preferences state.
      * @type {?CrSettingsPrefsElement}
      */
     prefs: Object,
 
     /** @type {?settings.DirectionDelegate} */
     directionDelegate: {
       observer: 'directionDelegateChanged_',
       type: Object,
     },
   },
 
+  listeners: {
+    'iron-select': 'onIronSelect_',

[dschuyler, 2016/05/03 22:57:56]

I may be misunderstanding, but it looks like
iron-select may be fired from a variety of 
elements (unlike the paper-responsive-change
which looks like it's only for the drawer).

Is it reasonable or useful to scope (qualify)
this more? Though maybe it's not a big deal
to remove .narrowing on other things. WDYT

[Dan Beam, 2016/05/03 23:28:37]

Done.

+    'paper-responsive-change': 'onPaperResponsiveChange_',
+  },
+
+  /** @private */
+  onIronSelect_: function() {
+    this.classList.remove('narrowing');
+  },
+
+  /**
+   * @param {!Event} e
+   * @private
+   */
+  onPaperResponsiveChange_: function(e) {
+    e = /** @type {{detail: {narrow: boolean}}} */(e);
+    this.classList.toggle('narrowing', e.detail.narrow);
+  },
+
   /** @private */
   directionDelegateChanged_: function() {
     this.$.panel.rightDrawer = this.directionDelegate.isRtl();
   },
 });