Make Service own ServiceContext.

services/user/user_shell_client.cc

Index: services/user/user_shell_client.cc
diff --git a/services/user/user_shell_client.cc b/services/user/user_shell_client.cc
index 75cac6dbca01fc127c60dcfc0876c9275db6e663..d91a39fa4c49321c013dd08cddd94fbd222a2a4e 100644
--- a/services/user/user_shell_client.cc
+++ b/services/user/user_shell_client.cc
@@ -88,9 +88,7 @@ UserShellClient::~UserShellClient() {
   leveldb_service_runner_->DeleteSoon(FROM_HERE, leveldb_objects_.release());
 }
 
-void UserShellClient::OnStart(shell::Connector* connector,
-                              const shell::Identity& identity,
-                              uint32_t id) {
+void UserShellClient::OnStart(const shell::Identity& identity) {
   user_objects_.reset(new UserShellClient::UserServiceObjects(
       GetUserDirForUserId(identity.user_id())));
   leveldb_objects_.reset(