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

mash/screenlock/screenlock.cc

Index: mash/screenlock/screenlock.cc
diff --git a/mash/screenlock/screenlock.cc b/mash/screenlock/screenlock.cc
index 42f2b0453f3f9871170137726b585b2c33925734..60f6f1ea3d6fc4b6e18d2afc91889ff2f08834a9 100644
--- a/mash/screenlock/screenlock.cc
+++ b/mash/screenlock/screenlock.cc
@@ -75,9 +75,10 @@ class ScreenlockView : public views::WidgetDelegateView,
 Screenlock::Screenlock() {}
 Screenlock::~Screenlock() {}
 
-void Screenlock::Initialize(mojo::Connector* connector, const std::string& url,
-                            const std::string& user_id, uint32_t id) {
-  tracing_.Initialize(connector, url);
+void Screenlock::Initialize(mojo::Connector* connector,
+                            const mojo::Identity& identity,
+                            uint32_t id) {
+  tracing_.Initialize(connector, identity.name());
 
   mash::shell::mojom::ShellPtr mash_shell;
   connector->ConnectToInterface("mojo:mash_shell", &mash_shell);