[Merge to 2785] Hide the DIV containing password import/export buttons

chrome/browser/resources/options/password_manager.html

 <div id="password-manager" class="page" hidden>
   <div class="close-button"></div>
   <h1 i18n-content="passwordsPage"></h1>
   <div class="content-area">
     <div class="password-manager-home">
       <div id="auto-signin-block" class="checkbox" hidden>
         <label>
           <input pref="credentials_enable_autosignin" type="checkbox">
           <span i18n-content="autoSigninTitle"></span>
         </label>
@@ skipping 10 matching lines @@
               i18n-values="placeholder:passwordSearchPlaceholder" incremental>
         </div>
       </div>
       <list id="saved-passwords-list" class="settings-list"></list>
       <div id="saved-passwords-list-empty-placeholder"
            class="settings-list-empty" hidden>
         <span i18n-content="passwordsNoPasswordsDescription"></span>
         <a target="_blank" i18n-content="learnMore"
            i18n-values="href:passwordManagerLearnMoreURL"></a>
       </div>
-      <div class="action-area">
+      <div id="password-manager-import-export" class="action-area" hidden>
         <div class="button-strip">
           <button id="password-manager-import" class="password-manager-home"
-              i18n-content="passwordManagerImportPasswordButtonText" hidden>
+              i18n-content="passwordManagerImportPasswordButtonText">
           </button>
           <button id="password-manager-export" class="password-manager-home"
-              i18n-content="passwordManagerExportPasswordButtonText" hidden>
+              i18n-content="passwordManagerExportPasswordButtonText">
           </button>
         </div>
       </div>
       <h3 i18n-content="passwordExceptionsTitle"></h3>
       <list id="password-exceptions-list" class="settings-list"></list>
       <div id="password-exceptions-list-empty-placeholder" hidden
            class="settings-list-empty">
         <span i18n-content="passwordsNoExceptionsDescription"></span>
         <a id="exceptions-learn-more" target="_blank" i18n-content="learnMore"
            i18n-values="href:passwordManagerLearnMoreURL"></a>
       </div>
     </div>
   </div>
   <div class="action-area">
     <span id="manage-passwords-span">
       <span i18n-content="passwordsManagePasswordsBeforeLinkText"></span>
       <a id="manage-passwords-link" target="_blank"
          i18n-content="passwordsManagePasswordsLinkText"
          i18n-values="href:passwordsManagePasswordsLink"></a>
       <span i18n-content="passwordsManagePasswordsAfterLinkText"></span>
     </span>
     <div class="spacer-div"></div>
     <div class="button-strip">
       <button id="password-manager-confirm" class="password-manager-home"
           i18n-content="done"></button>
     </div>
   </div>
 </div>