MD Settings: Use appropriate icon for "manage certificates" button.

chrome/browser/resources/settings/privacy_page/privacy_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/policy/cr_policy_vars_css.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout-classes.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="/clear_browsing_data_dialog/clear_browsing_data_dialog.html">
 <link rel="import" href="/controls/settings_checkbox.html">
 <link rel="import" href="/controls/settings_toggle_button.html">
@@ skipping 143 matching lines @@
           </settings-toggle-button>
         </div>
 </if>
 <if expr="use_nss_certs or is_win or is_macosx">
         <div id="manageCertificates" class="settings-box two-line"
             actionable on-tap="onManageCertificatesTap_">
           <div class="start">
             <div>$i18n{manageCertificates}</div>
             <div class="secondary">$i18n{manageCertificatesDescription}</div>
           </div>
-          <button class="subpage-arrow" is="paper-icon-button-light"></button>
+<if expr="use_nss_certs">
+          <button is="paper-icon-button-light" class="subpage-arrow"></button>
+</if>
+<if expr="not use_nss_certs">
+          <button is="paper-icon-button-light" class="icon-external"></button>
+</if>
         </div>
 </if>
         <div id="site-settings-subpage-trigger"
             class="settings-box two-line" actionable
             on-tap="onSiteSettingsTap_">
           <div class="start">
             <div>[[siteSettingsPageTitle_()]]</div>
             <div class="secondary">$i18n{siteSettingsDescription}</div>
           </div>
           <button class="subpage-arrow" is="paper-icon-button-light"></button>
@@ skipping 220 matching lines @@
             $i18n{siteSettingsCookieRemoveAll}
           </paper-button>
           <site-data-details-subpage page-title="{{pageTitle}}">
           </site-data-details-subpage>
         </settings-subpage>
       </template>
     </settings-animated-pages>
   </template>
   <script src="privacy_page.js"></script>
 </dom-module>