MD Settings: add 'preserve-focus' flag to fix iron-list focus bugs.

chrome/browser/resources/settings/search_engines_page/search_engines_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 
 <link rel="import" href="chrome://resources/html/action_link.html">
 <link rel="import" href="chrome://resources/html/action_link_css.html">
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/cr/ui/focus_without_ink.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="search_engines_browser_proxy.html">
 <link rel="import" href="search_engine_dialog.html">
@@ skipping 34 matching lines @@
       $i18n{searchEnginesNoOtherEngines}
     </div>
     <settings-search-engines-list id="otherEngines" engines="[[otherEngines]]"
           hide-headers scroll-target="[[subpageScrollTarget]]">
     </settings-search-engines-list>
     <template is="dom-if" if="[[showExtensionsList_]]">
       <div class="settings-box first">
         <h2>$i18n{searchEnginesExtension}</h2>
       </div>
       <iron-list id="extensions" class="extension-engines fixed-height-list"
-          items="[[extensions]]">
+          items="[[extensions]]" preserve-focus>
         <template>
           <settings-omnibox-extension-entry engine="[[item]]"
               tabindex$="[[tabIndex]]" iron-list-tab-index="[[tabIndex]]"
               last-focused="{{omniboxExtensionlastFocused_}}">
           </settings-omnibox-extension-entry>
         </template>
       </iron-list>
     </template>
   </template>
   <script src="search_engines_page.js"></script>
 </dom-module>