MD Settings: make iron list offset so items render onscreen

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/cr.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">
 <link rel="import" href="search_engines_list.html">
 <link rel="import" href="omnibox_extension_entry.html">
 <link rel="import" href="../global_scroll_target_behavior.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-search-engines-page">
   <template>
     <style include="settings-shared action-link">
       .extension-engines,
       #noOtherEngines {
         @apply(--settings-list-frame-padding);
       }
 
       settings-omnibox-extension-entry {
         border-top: var(--settings-separator-line);
       }
     </style>
     <div class="settings-box first">
       <h2>$i18n{searchEnginesDefault}</h2>
     </div>
-    <settings-search-engines-list engines="[[defaultEngines]]">
+    <settings-search-engines-list id="defaultEngines"
+        engines="[[defaultEngines]]">
     </settings-search-engines-list>
     <template is="dom-if" if="[[showAddSearchEngineDialog_]]" restamp>
       <settings-search-engine-dialog></settings-search-engine-dialog>
     </template>
 
     <div class="settings-box first">
       <h2 class="start">$i18n{searchEnginesOther}</h2>
       <paper-button class="secondary-button header-aligned-button"
           on-tap="onAddSearchEngineTap_" id="addSearchEngine">
         $i18n{add}
       </paper-button>
     </div>
     <div id="noOtherEngines" hidden="[[otherEngines.length]]">
       $i18n{searchEnginesNoOtherEngines}
     </div>
-    <settings-search-engines-list engines="[[otherEngines]]" hide-headers
-          scroll-target="[[subpageScrollTarget]]">
+    <settings-search-engines-list id="otherEngines" engines="[[otherEngines]]"
+          hide-headers scroll-target="[[subpageScrollTarget]]">
     </settings-search-engines-list>
     <template is="dom-if" if="[[showExtensionsList_]]">
       <div class="settings-box first">
         <h2>$i18n{searchEnginesExtension}</h2>
       </div>
       <iron-list id="extensions" class="extension-engines fixed-height-list"
           selectable items="[[extensions]]">
         <template>
           <settings-omnibox-extension-entry engine="[[item]]"
               tabindex$="[[tabIndex]]">
           </settings-omnibox-extension-entry>
         </template>
       </iron-list>
     </template>
   </template>
   <script src="search_engines_page.js"></script>
 </dom-module>