mash: Prerequisites for removing ShelfDelegate.

ash/shelf/shelf_application_menu_model.cc

Index: ash/shelf/shelf_application_menu_model.cc
diff --git a/ash/shelf/shelf_application_menu_model.cc b/ash/shelf/shelf_application_menu_model.cc
index 503ce9b83cc256932e55cdb95c05b8a79f457cdb..d991f340ce9f6aa059aa9cdb835a055ff2937f49 100644
--- a/ash/shelf/shelf_application_menu_model.cc
+++ b/ash/shelf/shelf_application_menu_model.cc
@@ -57,10 +57,10 @@ bool ShelfApplicationMenuModel::IsCommandIdEnabled(int command_id) const {
 
 void ShelfApplicationMenuModel::ExecuteCommand(int command_id,
                                                int event_flags) {
-  DCHECK(delegate_);
   DCHECK(IsCommandIdEnabled(command_id));
   // Have the delegate execute its own custom command id for the given item.
-  delegate_->ExecuteCommand(items_[command_id]->command_id, event_flags);
+  if (delegate_)
+    delegate_->ExecuteCommand(items_[command_id]->command_id, event_flags);
   RecordMenuItemSelectedMetrics(command_id, items_.size());
 }