Add additional CHECKs to AppListModel.

ui/app_list/app_list_item_list.cc

Index: ui/app_list/app_list_item_list.cc
diff --git a/ui/app_list/app_list_item_list.cc b/ui/app_list/app_list_item_list.cc
index 801f923ae2880c961e1776802db5f38f1cac6f7f..c8d96e2aec1a7c35ffd54ebf6079fbdd45f21b98 100644
--- a/ui/app_list/app_list_item_list.cc
+++ b/ui/app_list/app_list_item_list.cc
@@ -166,17 +166,15 @@ void AppListItemList::DeleteItem(const std::string& id) {
   // |item| will be deleted on destruction.
 }
 
-scoped_ptr<AppListItem> AppListItemList::RemoveItem(
-    const std::string& id) {
+scoped_ptr<AppListItem> AppListItemList::RemoveItem(const std::string& id) {
   size_t index;
-  if (FindItemIndex(id, &index))
-    return RemoveItemAt(index);
-
-  return scoped_ptr<AppListItem>();
+  if (!FindItemIndex(id, &index))
+    LOG(FATAL) << "RemoveItem: Not found: " << id;
+  return RemoveItemAt(index);
 }
 
 scoped_ptr<AppListItem> AppListItemList::RemoveItemAt(size_t index) {
-  DCHECK_LT(index, item_count());
+  CHECK_LT(index, item_count());
   AppListItem* item = app_list_items_[index];
   app_list_items_.weak_erase(app_list_items_.begin() + index);
   FOR_EACH_OBSERVER(AppListItemListObserver,