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

mash/screenlock/screenlock.h

Index: mash/screenlock/screenlock.h
diff --git a/mash/screenlock/screenlock.h b/mash/screenlock/screenlock.h
index e6c06119176957e2802fc14435748005dc036e1b..f1d2755dd5c768b4345b52c30d5b395a14a09fdc 100644
--- a/mash/screenlock/screenlock.h
+++ b/mash/screenlock/screenlock.h
@@ -29,8 +29,9 @@ class Screenlock : public mojo::ShellClient,
 
  private:
   // mojo::ShellClient:
-  void Initialize(mojo::Connector* connector, const std::string& url,
-                  const std::string& user_id, uint32_t id) override;
+  void Initialize(mojo::Connector* connector,
+                  const mojo::Identity& identity,
+                  uint32_t id) override;
 
   // mash::shell::mojom::ScreenlockStateListener:
   void ScreenlockStateChanged(bool locked) override;