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

chrome/browser/resources/settings/a11y_page/a11y_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/core-menu/core-menu.html">
 <link rel="import" href="chrome://resources/polymer/paper-item/paper-item.html">
 <link rel="import" href="chrome://resources/polymer/paper-shadow/paper-shadow.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_checkbox/cr_checkbox.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_dropdown_menu/cr_dropdown_menu.html">
 <link rel="import" href="chrome://md-settings/settings_page/settings_page_header.html">
 
 <polymer-element name="cr-settings-a11y-page">
   <template>
     <link rel="stylesheet" href="chrome://md-settings/settings_page/settings_page.css">
     <link rel="stylesheet" href="a11y_page.css">
     <paper-shadow layout vertical cross-fade>
       <cr-settings-page-header page="{{}}"></cr-settings-page-header>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.a11y.enableMenu}}" for>
+        <cr-checkbox checked="{{prefs.settings.a11y.enableMenu.value}}" for>
         </cr-checkbox>
         <span>Show accessibility options in the system menu</span>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.a11y.largeCursorEnabled}}" for>
+        <cr-checkbox checked="{{prefs.settings.a11y.largeCursorEnabled.value}}" for>
         </cr-checkbox>
         <span>Show large mouse cursor</span>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.a11y.highContrastEnabled}}" for>
+        <cr-checkbox checked="{{prefs.settings.a11y.highContrastEnabled.value}}" for>
         </cr-checkbox>
         <span>Use high contrast mode</span>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.a11y.stickyKeysEnabled}}" for>
+        <cr-checkbox checked="{{prefs.settings.a11y.stickyKeysEnabled.value}}" for>
         </cr-checkbox>
         <span>Enable sticky keys</span>
         <span class="sub-label">
           (to perform keyboard shortcuts by typing them sequentially)
         </span>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.accessibility}}" for>
+        <cr-checkbox checked="{{prefs.settings.accessibility.value}}" for>
         </cr-checkbox>
         <span>Enable ChromeVox</span>
         <span class="sub-label">
           (spoken feedback)
         </span>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.a11y.screenMagnifier}}" for>
+        <cr-checkbox checked="{{prefs.settings.a11y.screenMagnifier.value}}" for>
         </cr-checkbox>
         <span>Enable screen magnifier</span>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.touchpad.enableTapDragging}}" for>
+        <cr-checkbox checked="{{prefs.settings.touchpad.enableTapDragging.value}}" for>
         </cr-checkbox>
         <span>Enable tap dragging</span>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.a11y.autoclick}}" for>
+        <cr-checkbox checked="{{prefs.settings.a11y.autoclick.value}}" for>
         </cr-checkbox>
         <span>Automatically click when the mouse pointer stops</span>
       </core-label>
       <core-label horizontal layout center class="autoclick-delay-label"
-       hidden?="{{!prefs.settings.a11y.autoclick}}">
+       hidden?="{{!prefs.settings.a11y.autoclick.value}}">
         <span>Delay before click:</span>
         <cr-dropdown-menu class="autoclick-dropdown">
           <core-menu class="menu" valueAttr="value" selectedAttribute=""
-              selected="{{prefs.settings.a11y.autoclickDelayMs}}">
+              selected="{{prefs.settings.a11y.autoclickDelayMs.value}}">
             <paper-item value="200">extremely short</paper-item>
             <paper-item value="400">very short</paper-item>
             <paper-item value="600">short</paper-item>
             <paper-item value="800">long</paper-item>
             <paper-item value="1000">very long</paper-item>
           </core-menu>
         </cr-dropdown-menu>
       </core-label>
       <core-label horizontal layout>
-        <cr-checkbox checked="{{prefs.settings.a11y.virtualKeyboard}}" for>
+        <cr-checkbox checked="{{prefs.settings.a11y.virtualKeyboard.value}}" for>
         </cr-checkbox>
         <span>Enable on-screen keyboard</span>
       </core-label>
     </paper-shadow>
   </template>
   <script src="a11y_page.js"></script>
 </polymer-element>