Moves WorkspaceController to ash/common

ash/mus/root_window_controller.cc

Index: ash/mus/root_window_controller.cc
diff --git a/ash/mus/root_window_controller.cc b/ash/mus/root_window_controller.cc
index a0b727c6d83592652653b90e60d662089a7f673c..dfe6c94fb743aed1de1e0c017621467db7097885 100644
--- a/ash/mus/root_window_controller.cc
+++ b/ash/mus/root_window_controller.cc
@@ -82,7 +82,9 @@ RootWindowController::RootWindowController(WindowManager* window_manager,
       new AlwaysOnTopController(always_on_top_container));
 }
 
-RootWindowController::~RootWindowController() {}
+RootWindowController::~RootWindowController() {
+  root_window_controller_common_->DeleteWorkspaceController();
+}
 
 shell::Connector* RootWindowController::GetConnector() {
   return window_manager_->connector();