[WebUI] use one-way Polymer binding on dom-if, dom-repeat, and iron-list

chrome/browser/resources/md_downloads/manager.html

 <link rel="import" href="chrome://resources/cr_elements/hidden_style_css.html">
 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/cr/ui.html">
 <link rel="import" href="chrome://resources/html/cr/ui/command.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-a11y-announcer/iron-a11y-announcer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://downloads/action_service.html">
 <link rel="import" href="chrome://downloads/constants.html">
@@ skipping 75 matching lines @@
             url(chrome://downloads/2x/no_downloads.png) 2x)
             no-repeat center center;
         height: 144px;  /* Matches natural image height. */
         margin-bottom: 32px;
       }
     </style>
 
     <downloads-toolbar id="toolbar" spinner-active="{{spinnerActive_}}"
         role="none">
     </downloads-toolbar>
-    <iron-list id="downloads-list" items="{{items_}}"
+    <iron-list id="downloads-list" items="[[items_]]"
         hidden="[[!hasDownloads_]]">
       <template>
         <downloads-item data="[[item]]"></downloads-item>
       </template>
     </iron-list>
     <div id="no-downloads" hidden="[[hasDownloads_]]">
       <div>
         <div class="illustration"></div>
         <span>[[noDownloadsText_(inSearchMode_)]]</span>
       </div>
     </div>
   </template>
   <script src="chrome://downloads/manager.js"></script>
 </dom-module>