buffet: Multiple listeners of add/remove new command.

Replace CommandDispatchInterface with callbacks.
Lists of callbacks in CommandQueue.

BUG=brillo:697
TEST=FEATURE=test emerge-gizmo buffet

Change-Id: I3c164c8c7c2cb098b896aa8d5c9a99d856b05172
Reviewed-on: https://chromium-review.googlesource.com/270350
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/device_registration_info_unittest.cc b/buffet/device_registration_info_unittest.cc
index 1800da1..ec68b21 100644
--- a/buffet/device_registration_info_unittest.cc
+++ b/buffet/device_registration_info_unittest.cc
@@ -188,7 +188,7 @@
     storage_ = std::make_shared<MemStorage>();
     storage_->Save(&data_);
     transport_ = std::make_shared<chromeos::http::fake::Transport>();
-    command_manager_ = std::make_shared<CommandManager>(nullptr);
+    command_manager_ = std::make_shared<CommandManager>();
     state_manager_ = std::make_shared<StateManager>(&mock_state_change_queue_);
     chromeos::KeyValueStore config_store;
     config_store.SetString("client_id", test_data::kClientId);