[CrOS Settings] Change opacity when account whitelist is disabled.

Change-Id: I022f2aa29b468a43d2dbfecac5275575b9317e57
Bug: 825150
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660880
Commit-Queue: Regan Hsu <hsuregan@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670245}

chrome/browser/resources/settings/people_page/user_list.html

@@ -36,6 +36,10 @@
       .user-info {
         padding-inline-start: 20px;
       }
+
+      :host([disabled]) .user-list {
+        opacity: var(--cr-disabled-opacity);
+      }
     </style>
     <div class="user-list" scrollable>
       <template is="dom-repeat" items="[[users_]]">

chrome/browser/resources/settings/people_page/user_list.js

@@ -42,6 +42,7 @@ Polymer({
     disabled: {
       type: Boolean,
       value: false,
+      reflectToAttribute: true,
     }
   },