MD Settings: hide some things from the a11y tree with role="none" so VoiceOver navigation works

chrome/browser/resources/settings/settings_ui/settings_ui.html

 <link rel="import" href="chrome://resources/cr_elements/cr_drawer/cr_drawer.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_toolbar/cr_toolbar.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-header-panel/paper-header-panel.html">
 <link rel="import" href="../direction_delegate.html">
 <link rel="import" href="../global_scroll_target_behavior.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../icons.html">
@@ skipping 64 matching lines @@
       }
     </style>
     <settings-prefs id="prefs" prefs="{{prefs}}"></settings-prefs>
     <cr-toolbar page-name="$i18n{settings}"
         clear-label="$i18n{clearSearch}"
         search-prompt="$i18n{searchPrompt}"
         on-cr-toolbar-menu-tap="onMenuButtonTap_"
         spinner-active="[[toolbarSpinnerActive_]]"
         menu-label="$i18n{menuButtonLabel}"
         on-search-changed="onSearchChanged_"
+        role="none"
         show-menu>
     </cr-toolbar>
     <dialog id="drawer" is="cr-drawer">
       <div class="drawer-header" tabindex="-1">$i18n{settings}</div>
       <div class="drawer-content">
         <template is="dom-if" id="drawerTemplate">
           <settings-menu page-visibility="[[pageVisibility_]]"
               show-android-apps="[[showAndroidApps_]]"
               on-iron-activate="onIronActivate_"
               advanced-opened="{{advancedOpened_}}">
           </settings-menu>
         </template>
       </div>
     </dialog>
-    <paper-header-panel id="headerPanel" mode="waterfall">
+    <paper-header-panel id="headerPanel" mode="waterfall" role="none">
       <settings-main id="main" prefs="{{prefs}}"
           toolbar-spinner-active="{{toolbarSpinnerActive_}}"
           page-visibility="[[pageVisibility_]]"
           show-android-apps="[[showAndroidApps_]]"
           advanced-toggle-expanded="{{advancedOpened_}}">
       </settings-main>
     </paper-header-panel>
   </template>
   <script src="settings_ui.js"></script>
 </dom-module>