Don't dispatch event after shutdown on AshWTHUnified

ash/display/mirror_window_controller.cc

Index: ash/display/mirror_window_controller.cc
diff --git a/ash/display/mirror_window_controller.cc b/ash/display/mirror_window_controller.cc
index 8fb7767a94df5345b67b8f8e66be6cc19b0f4e32..3e7df2d79b23d1735fe7ca50db75e368c0c3cd9f 100644
--- a/ash/display/mirror_window_controller.cc
+++ b/ash/display/mirror_window_controller.cc
@@ -145,7 +145,7 @@ void MirrorWindowController::UpdateWindow(
       mirror_window->SetBounds(host->window()->bounds());
       mirror_window->Show();
       if (reflector_) {
-        // TODO(oshima): Enable this once reflect change is landed.
+        // TODO(oshima): Enable this once reflector change is landed.
         // reflector_->AddMirroringLayer(mirror_window->layer());
       } else {
         reflector_ =
@@ -267,7 +267,9 @@ void MirrorWindowController::CloseAndDeleteHost(MirroringHostInfo* host_info) {
 
   host->RemoveObserver(Shell::GetInstance()->display_controller());
   host->RemoveObserver(this);
-  // reflector_->RemoveMirroringLayer(host_info->mirror_window->layer());
+  host_info->ash_host->PrepareForShutdown();
+  // TODO(oshima): Enable this once reflector change is landed.
+  // reflector_->RemovedMirroringLayer(mirror_window->layer());
   delete host_info;
 }