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

mojo/shell/public/cpp/shell_connection.h

Index: mojo/shell/public/cpp/shell_connection.h
diff --git a/mojo/shell/public/cpp/shell_connection.h b/mojo/shell/public/cpp/shell_connection.h
index 8e2f980ae756e285a0cd7c6a8233a86f00f27243..7ec245b33b3f0ef327843f0b19e1d30f7eae5b2d 100644
--- a/mojo/shell/public/cpp/shell_connection.h
+++ b/mojo/shell/public/cpp/shell_connection.h
@@ -59,13 +59,11 @@ class ShellConnection : public shell::mojom::ShellClient {
  private:
   // shell::mojom::ShellClient:
   void Initialize(shell::mojom::ConnectorPtr connector,
-                  const String& name,
-                  const String& user_id,
+                  shell::mojom::IdentityPtr identity,
                   uint32_t id) override;
   void AcceptConnection(
-      const String& requestor_name,
-      const String& requestor_user_id,
-      uint32_t requestor_id,
+      shell::mojom::IdentityPtr source,
+      uint32_t source_id,
       shell::mojom::InterfaceProviderRequest remote_interfaces,
       shell::mojom::InterfaceProviderPtr local_interfaces,
       Array<String> allowed_interfaces,