MD Settings: Fix rendering of popup menus inside iron-lists.

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

 <link rel="import" href="chrome://resources/html/action_link.html">
 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_expand_button/cr_expand_button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-collapse/iron-collapse.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="/search_engines_page/search_engines_browser_proxy.html">
 <link rel="import" href="/search_engines_page/search_engine_dialog.html">
 <link rel="import" href="/search_engines_page/search_engines_list.html">
 <link rel="import" href="/search_engines_page/omnibox_extension_entry.html">
 <link rel="import" href="/settings_shared_css.html">
 
 <dom-module id="settings-search-engines-page">
   <link rel="import" type="css" href="chrome://resources/css/action_link.css">
   <template>
     <style include="settings-shared">
       .extension-engines {
         @apply(--settings-list-frame-padding);
       }
 
       settings-omnibox-extension-entry {
         border-top: var(--settings-separator-line);
       }
 
       settings-omnibox-extension-entry:first-of-type {
         border-top: none;
       }
+
+      #extensions-container {
+        overflow: inherit;
+      }
     </style>
     <div class="settings-box first">
       <h2>$i18n{searchEnginesDefault}</h2>
     </div>
     <settings-search-engines-list engines="[[defaultEngines]]">
     </settings-search-engines-list>
     <template is="dom-if" if="[[showAddSearchEngineDialog_]]" restamp>
       <settings-search-engine-dialog></settings-search-engine-dialog>
     </template>
     <div class="settings-box first">
       <h2>$i18n{searchEnginesOther}</h2>
     </div>
     <!-- TODO(dbeam): why does on-click work with keyboard but on-tap
          doesn't? -->
     <settings-search-engines-list engines="[[otherEngines]]">
       <a class="list-item list-button" is="action-link"
           on-tap="onAddSearchEngineTap_" id="addSearchEngine">
           $i18n{searchEnginesAddSearchEngine}</a>
     </settings-search-engines-list>
 
     <template is="dom-if" if="[[showExtensionsList_]]">
       <div class="settings-box first">
         <h2>$i18n{searchEnginesExtension}</h2>
       </div>
-      <iron-list id="extensions" class="extension-engines" selectable
-          items="[[extensions]]">
-        <template>
-          <settings-omnibox-extension-entry engine="[[item]]"
-              tabindex$="[[tabIndex]]">
-          </settings-omnibox-extension-entry>
-        </template>
-      </iron-list>
+      <div id="extensions-container">
+        <iron-list id="extensions" class="extension-engines" selectable
+            items="[[extensions]]" scroll-target="extensions-container">
+          <template>
+            <settings-omnibox-extension-entry engine="[[item]]"
+                tabindex$="[[tabIndex]]">
+            </settings-omnibox-extension-entry>
+          </template>
+        </iron-list>
+      </div>
     </template>
   </template>
   <script src="search_engines_page.js"></script>
 </dom-module>