Example of usage of new features of context and screen.

chrome/browser/resources/login/screen.js

Index: chrome/browser/resources/login/screen.js
diff --git a/chrome/browser/resources/login/screen.js b/chrome/browser/resources/login/screen.js
index 6bbf1f35489b8f8470faeb82882151e5e8c55289..f0f0a5fa4eb30a5bdf6440cae12ca60bca8fe60f 100644
--- a/chrome/browser/resources/login/screen.js
+++ b/chrome/browser/resources/login/screen.js
@@ -54,7 +54,7 @@ cr.define('login', function() {
      */
     send: function(messageName, varArgs) {
       if (arguments.length == 0)
-        throw Error('Message name is not provided.');
+        throw Error("Message name is not provided.");
       var fullMessageName = this.sendPrefix_ + messageName;
       var payload = Array.prototype.slice.call(arguments, 1);
       chrome.send(fullMessageName, payload);
@@ -227,6 +227,7 @@ cr.define('login', function() {
           screen.contextChanged_.apply(screen, arguments);
         }
         constructor.prototype.name = function() { return id; };
+        constructor.prototype.sendPrefix_ = 'login.' + name + '.';
 
         constructor.register = function() {
           var screen = $(id);