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

mojo/shell/public/cpp/lib/shell_client.cc

Index: mojo/shell/public/cpp/lib/shell_client.cc
diff --git a/mojo/shell/public/cpp/lib/shell_client.cc b/mojo/shell/public/cpp/lib/shell_client.cc
index f5441ce12e11a0dde156c74fa2c7d030867f033f..c41999bfe6d6906eb42532de9bd10c9aacb16c1c 100644
--- a/mojo/shell/public/cpp/lib/shell_client.cc
+++ b/mojo/shell/public/cpp/lib/shell_client.cc
@@ -9,8 +9,8 @@ namespace mojo {
 ShellClient::ShellClient() {}
 ShellClient::~ShellClient() {}
 
-void ShellClient::Initialize(Connector* connector, const std::string& name,
-                             const std::string& user_id, uint32_t id) {
+void ShellClient::Initialize(Connector* connector, const Identity& identity,
+                             uint32_t id) {
 }
 
 bool ShellClient::AcceptConnection(Connection* connection) {