ash: Remove ShelfModel id conversion functions.

chrome/browser/ui/ash/launcher/arc_app_deferred_launcher_controller.cc

Index: chrome/browser/ui/ash/launcher/arc_app_deferred_launcher_controller.cc
diff --git a/chrome/browser/ui/ash/launcher/arc_app_deferred_launcher_controller.cc b/chrome/browser/ui/ash/launcher/arc_app_deferred_launcher_controller.cc
index ea088d259a95216c6da5764382af20845fef2a4c..453d3cff02801d6084a26d1931bd600cf3b21b9b 100644
--- a/chrome/browser/ui/ash/launcher/arc_app_deferred_launcher_controller.cc
+++ b/chrome/browser/ui/ash/launcher/arc_app_deferred_launcher_controller.cc
@@ -111,7 +111,7 @@ void ArcAppDeferredLauncherController::Close(const std::string& app_id) {
   if (it == app_controller_map_.end())
     return;
 
-  const ash::ShelfID shelf_id = owner_->GetShelfIDForAppID(shelf_app_id);
+  const ash::ShelfID shelf_id(shelf_app_id);
   const bool need_close_item =
       it->second == owner_->shelf_model()->GetShelfItemDelegate(shelf_id);
   app_controller_map_.erase(it);
@@ -197,7 +197,7 @@ void ArcAppDeferredLauncherController::RegisterDeferredLaunch(
 
   const std::string shelf_app_id =
       ArcAppWindowLauncherController::GetShelfAppIdFromArcAppId(app_id);
-  const ash::ShelfID shelf_id = owner_->GetShelfIDForAppID(shelf_app_id);
+  const ash::ShelfID shelf_id(shelf_app_id);
 
   // We are allowed to apply new deferred controller only over non-active items.
   const ash::ShelfItem* item = owner_->GetItem(shelf_id);
@@ -208,7 +208,7 @@ void ArcAppDeferredLauncherController::RegisterDeferredLaunch(
       base::MakeUnique<ArcAppDeferredLauncherItemController>(
           shelf_app_id, event_flags, weak_ptr_factory_.GetWeakPtr());
   ArcAppDeferredLauncherItemController* item_controller = controller.get();
-  if (shelf_id.IsNull()) {
+  if (item == nullptr) {
     owner_->CreateAppLauncherItem(std::move(controller), ash::STATUS_RUNNING);
   } else {
     owner_->shelf_model()->SetShelfItemDelegate(shelf_id,