AppListModel / AppsGridView: Better error handling for corner cases.

ui/app_list/app_list_model.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/app_list/app_list_model.h"
 
 #include <string>
 
 #include "ui/app_list/app_list_folder_item.h"
 #include "ui/app_list/app_list_item.h"
@@ skipping 73 matching lines @@
   return AddItemToFolderItemAndNotify(dest_folder, item.Pass());
 }
 
 const std::string AppListModel::MergeItems(const std::string& target_item_id,
                                            const std::string& source_item_id) {
   if (!folders_enabled()) {
     LOG(ERROR) << "MergeItems called with folders disabled.";
     return "";
   }
   DVLOG(2) << "MergeItems: " << source_item_id << " -> " << target_item_id;
+
+  if (target_item_id == source_item_id) {
+    LOG(WARNING) << "MergeItems tried to drop item onto itself ("
+                 << source_item_id << " -> " << target_item_id << ").";
+    return "";
+  }
+
   // Find the target item.
-  AppListItem* target_item = FindItem(target_item_id);
+  AppListItem* target_item = top_level_item_list_->FindItem(target_item_id);
   if (!target_item) {
     LOG(ERROR) << "MergeItems: Target no longer exists.";
     return "";
   }
-  CHECK(target_item->folder_id().empty());
 
   AppListItem* source_item = FindItem(source_item_id);
   if (!source_item) {
     LOG(ERROR) << "MergeItems: Source no longer exists.";
     return "";
   }
 
   // If the target item is a folder, just add the source item to it.
   if (target_item->GetItemType() == AppListFolderItem::kItemType) {
     AppListFolderItem* target_folder =
         static_cast<AppListFolderItem*>(target_item);
     if (target_folder->folder_type() == AppListFolderItem::FOLDER_TYPE_OEM) {
       LOG(WARNING) << "MergeItems called with OEM folder as target";
       return "";
     }
     scoped_ptr<AppListItem> source_item_ptr = RemoveItem(source_item);
     source_item_ptr->set_position(
         target_folder->item_list()->CreatePositionBefore(
             syncer::StringOrdinal()));
     AddItemToFolderItemAndNotify(target_folder, source_item_ptr.Pass());
     return target_folder->id();
   }
 
   // Otherwise remove the source item and target item from their current
   // location, they will become owned by the new folder.
   scoped_ptr<AppListItem> source_item_ptr = RemoveItem(source_item);
   CHECK(source_item_ptr);
+  // Note: This would fail if |target_item_id == source_item_id|, except we
+  // checked that they are distinct at the top of this method.
   scoped_ptr<AppListItem> target_item_ptr =
       top_level_item_list_->RemoveItem(target_item_id);
   CHECK(target_item_ptr);
 
   // Create a new folder in the same location as the target item.
   std::string new_folder_id = AppListFolderItem::GenerateId();
   DVLOG(2) << "Creating folder for merge: " << new_folder_id;
   scoped_ptr<AppListItem> new_folder_ptr(new AppListFolderItem(
       new_folder_id, AppListFolderItem::FOLDER_TYPE_NORMAL));
   new_folder_ptr->set_position(target_item_ptr->position());
@@ skipping 246 matching lines @@
   scoped_ptr<AppListItem> result = folder->item_list()->RemoveItem(item->id());
   result->set_folder_id("");
   if (folder->item_list()->item_count() == 0) {
     DVLOG(2) << "Deleting empty folder: " << folder->ToDebugString();
     DeleteItem(folder_id);
   }
   return result.Pass();
 }
 
 }  // namespace app_list