Add a instance groups to Connect(), and introduce an Identity struct.

ash/mus/sysui_application.h

Index: ash/mus/sysui_application.h
diff --git a/ash/mus/sysui_application.h b/ash/mus/sysui_application.h
index 78d159904384c4a285f23ecdf3547189ac9aac47..dba0f5e3dc28d611a985b4767c302f017fa3b96b 100644
--- a/ash/mus/sysui_application.h
+++ b/ash/mus/sysui_application.h
@@ -23,8 +23,7 @@ class SysUIApplication : public mojo::ShellClient {
  private:
   // mojo::ShellClient:
   void Initialize(mojo::Connector* connector,
-                  const std::string& url,
-                  const std::string& user_id,
+                  const mojo::Identity& identity,
                   uint32_t id) override;
   bool AcceptConnection(mojo::Connection* connection) override;