Revert of [i18n] chromeos login i18n-content to $i18n{}

chrome/browser/resources/chromeos/login/header_bar.html

 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 
 <div id="login-header-bar" hidden
     class="login-header-bar-hidden layout horizontal">
   <div id="shutdown-header-bar-item" class="header-bar-item">
     <button id="shutdown-button" class="custom-appearance layout vertical">
-      <div id="shutdown-button-text" class="flex layout horizontal center">
-        $i18n{shutDown}
+      <div id="shutdown-button-text" class="flex layout horizontal center"
+          i18n-content="shutDown">
       </div>
     </button>
   </div>
   <div id="restart-header-bar-item" class="header-bar-item">
     <button id="restart-button" class="custom-appearance layout vertical">
-      <div id="restart-button-text" class="flex layout horizontal center">
-        $i18n{restart}
+      <div id="restart-button-text" class="flex layout horizontal center"
+          i18n-content="restart">
       </div>
     </button>
   </div>
   <div id="apps-header-bar-item" class="header-bar-item" hidden>
-    <button id="show-apps-button" class="custom-appearance">
-      $i18n{showApps}
+    <button id="show-apps-button" class="custom-appearance"
+        i18n-content="showApps">
     </button>
   </div>
   <div id="guest-user-header-bar-item" class="header-bar-item" hidden>
     <button id="guest-user-button" class="custom-appearance layout vertical">
-      <div id="guest-user-button-text" class="flex layout horizontal center">
-        $i18n{browseAsGuest}
+      <div id="guest-user-button-text" class="flex layout horizontal center"
+          i18n-content="browseAsGuest">
       </div>
     </button>
   </div>
   <div id="add-user-header-bar-item" class="header-bar-item" hidden>
     <button id="add-user-button" class="custom-appearance layout vertical">
-      <div id="add-user-button-text" class="flex layout horizontal center">
-        $i18n{addUser}
+      <div id="add-user-button-text" class="flex layout horizontal center"
+          i18n-content="addUser">
       </div>
     </button>
   </div>
   <div id="more-settings-header-bar-item" class="header-bar-item">
     <button id="more-settings-button" class="custom-appearance layout vertical">
       <div id="more-settings-button-text" class="flex layout horizontal center"
           i18n-values="aria-label:moreOptions">
       </div>
     </button>
     <button class="add-supervised-user-menu custom-appearance"
-        id="add-supervised-user-menu" tabindex="0">
-      $i18n{addSupervisedUser}
+        id="add-supervised-user-menu" tabindex="0"
+        i18n-content="addSupervisedUser">
     </button>
   </div>
   <div id="sign-out-user-item" class="header-bar-item" hidden>
     <button id="sign-out-user-button" class="custom-appearance layout vertical">
-      <div id="sign-out-user-button-text" class="flex layout horizontal center">
-        $i18n{signOutUser}
+      <div id="sign-out-user-button-text" class="flex layout horizontal center" 
+          i18n-content="signOutUser">
       </div>
     </button>
   </div>
   <div id="cancel-multiple-sign-in-item" class="header-bar-item" hidden>
     <button id="cancel-multiple-sign-in-button"
         class="custom-appearance layout vertical">
       <div id="cancel-multiple-sign-in-button-text"
-          class="flex layout horizontal center">$i18n{cancel}</div>
+          class="flex layout horizontal center" i18n-content="cancel">
+      </div>
     </button>
   </div>
 </div>