Fetch and actually set prefs (using chrome.send for now).

chrome/browser/resources/settings/downloads_page/downloads_page.html

 <link rel="import" href="chrome://resources/polymer/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/core-label/core-label.html">
 <link rel="import" href="chrome://resources/polymer/paper-input/paper-input.html">
 <link rel="import" href="chrome://resources/polymer/paper-shadow/paper-shadow.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_button/cr_button.
 html">
 <link rel="import" href="chrome://resources/cr_elements/cr_checkbox/cr_checkbox.
 html">
 <link rel="import" href="chrome://resources/cr_elements/cr_input/cr_input.html">
 
 <polymer-element name="cr-settings-downloads-page">
   <template>
     <link rel="stylesheet" href="chrome://md-settings/settings_page/settings_page.css">
     <link rel="stylesheet" href="downloads_page.css">
     <paper-shadow layout vertical cross-fade>
       <cr-settings-page-header page="{{}}"></cr-settings-page-header>
       <div horizontal layout center>
         <core-label horizontal layout center>
           <span class="location-label">Download location:</span>
           <cr-input id="downloadsPath" floatingLabel="false"
-              value="{{prefs.settings.download.defaultDirectory}}" readonly for>
+              value="{{prefs.settings.download.default_directory.value}}" readonly for>
           </cr-input>
         </core-label>
         <cr-button id="changeDownloadsPath"
             on-click="{{selectDownloadLocation}}">Change</cr-button>
       </div>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.download.promptForDownload}}" for>
+        <cr-checkbox checked="{{prefs.settings.download.prompt_for_download.value}}" for>
         </cr-checkbox>
         <span>Ask where to save each file before downloading</span>
       </core-label>
     </paper-shadow>
   </template>
   <script src="downloads_page.js"></script>
 </polymer-element>