Change userid from a uint32_t to a string guid

mash/shell/shell_application_delegate.cc

Index: mash/shell/shell_application_delegate.cc
diff --git a/mash/shell/shell_application_delegate.cc b/mash/shell/shell_application_delegate.cc
index c46f0e26fccdbbffe8927bd9fd1e1e60fbfe844b..6d02ee26c858553b0496d4bbeac85167076a407c 100644
--- a/mash/shell/shell_application_delegate.cc
+++ b/mash/shell/shell_application_delegate.cc
@@ -19,8 +19,8 @@ ShellApplicationDelegate::~ShellApplicationDelegate() {}
 
 void ShellApplicationDelegate::Initialize(mojo::Connector* connector,
                                           const std::string& url,
-                                          uint32_t id,
-                                          uint32_t user_id) {
+                                          const std::string& user_id,
+                                          uint32_t id) {
   connector_ = connector;
   StartBrowserDriver();
   StartWindowManager();