Change ExternalApplicationRegistrar::Register API

mojo/shell/external_application_registrar_connection.cc

Index: mojo/shell/external_application_registrar_connection.cc
diff --git a/mojo/shell/external_application_registrar_connection.cc b/mojo/shell/external_application_registrar_connection.cc
index 57498a9e16ab163215a79c41e69321788190a76a..62c49d6cea97fc40e05db2712fd9823b93e53fdc 100644
--- a/mojo/shell/external_application_registrar_connection.cc
+++ b/mojo/shell/external_application_registrar_connection.cc
@@ -53,11 +53,9 @@ void ExternalApplicationRegistrarConnection::Connect(
 
 void ExternalApplicationRegistrarConnection::Register(
     const GURL& app_url,
-    ShellPtr* shell,
-    base::Closure register_complete_callback) {
+    base::Callback<void(ShellPtr)> register_complete_callback) {
   DCHECK(!client_socket_);
-  registrar_->Register(
-      String::From(app_url), Get(shell), register_complete_callback);
+  registrar_->Register(String::From(app_url), register_complete_callback);
 }
 
 void ExternalApplicationRegistrarConnection::OnConnect(