Change userid from a uint32_t to a string guid

mash/example/window_type_launcher/window_type_launcher.cc

Index: mash/example/window_type_launcher/window_type_launcher.cc
diff --git a/mash/example/window_type_launcher/window_type_launcher.cc b/mash/example/window_type_launcher/window_type_launcher.cc
index d4fdc69931c3cf26e2b8c0643225ebf135530285..141bb3fd48eaa1abbe7019663c89273665f59524 100644
--- a/mash/example/window_type_launcher/window_type_launcher.cc
+++ b/mash/example/window_type_launcher/window_type_launcher.cc
@@ -357,7 +357,8 @@ WindowTypeLauncher::~WindowTypeLauncher() {}
 
 void WindowTypeLauncher::Initialize(mojo::Connector* connector,
                                     const std::string& url,
-                                    uint32_t id, uint32_t user_id) {
+                                    const std::string& user_id,
+                                    uint32_t id) {
   aura_init_.reset(new views::AuraInit(connector, "views_mus_resources.pak"));
 
   views::WindowManagerConnection::Create(connector);