Example of usage of new features of context and screen.

chrome/browser/ui/webui/chromeos/login/base_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
index 9efddca25312b298cf9845616bff6667ad0c7d6b..8f7a79bdd1dcd112e4bc23b03238a9960ea9cb02 100644
--- a/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/base_screen_handler.h
@@ -200,6 +200,12 @@ class BaseScreenHandler : public content::WebUIMessageHandler {
         name, base::Bind(&CallbackWrapper4<A1, A2, A3, A4>, callback));
   }
 
+  template <typename Method>
+  void AddPrefixedCallback(const std::string& unprefixed_name,
+                           const Method& method) {
+    AddCallback(FullMethodPath(unprefixed_name), method);
+  }
+
   // Called when the page is ready and handler can do initialization.
   virtual void Initialize() = 0;