[MD settings] replace secondary-action with separator

chrome/browser/resources/settings/search_page/search_page.html

Index: chrome/browser/resources/settings/search_page/search_page.html
diff --git a/chrome/browser/resources/settings/search_page/search_page.html b/chrome/browser/resources/settings/search_page/search_page.html
index f19514a35f9b635448916d5e9e76d69b9f481511..cf128c1ba7025d694afe15470282ef299bc1f4a0 100644
--- a/chrome/browser/resources/settings/search_page/search_page.html
+++ b/chrome/browser/resources/settings/search_page/search_page.html
@@ -88,8 +88,9 @@
                            hotwordInfo_.alwaysOn)]]"
                 on-change="onHotwordSearchEnableChange_">
             </settings-toggle-button>
-            <div class="secondary-action"
+            <div class="layout horizontal center"

[hcarmona, 2017/05/01 18:12:30]

Why don't other sections need these changes?

[dschuyler, 2017/05/01 19:12:08]

This is here for the sake of making a group to hide/show with the hidden$=
attribute. I would like to remove the dependency here and elsewhere on the
layout... classes. I'll look at that as another CL.

                 hidden$="[[!getShowHotwordSearchRetrain_(hotwordInfo_.*)]]">
+              <div class="separator"></div>
               <paper-button on-tap="onRetrainTap_" class="secondary-button">
                 $i18n{searchOkGoogleRetrain}
               </paper-button>