Use ChromeLauncherControllerImpl::GetItem; cleanup.

ash/common/shelf/shelf_model.cc

 // Copyright 2013 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 "ash/common/shelf/shelf_model.h"
 
 #include <algorithm>
 
 #include "ash/common/shelf/shelf_item_delegate.h"
 #include "ash/common/shelf/shelf_model_observer.h"
@@ skipping 72 matching lines @@
     return;
   // TODO: this needs to enforce valid ranges.
   ShelfItem item(items_[index]);
   items_.erase(items_.begin() + index);
   items_.insert(items_.begin() + target_index, item);
   for (auto& observer : observers_)
     observer.ShelfItemMoved(index, target_index);
 }
 
 void ShelfModel::Set(int index, const ShelfItem& item) {
-  DCHECK(index >= 0 && index < item_count());
+  if (index < 0 || index >= item_count()) {
+    NOTREACHED();
+    return;
+  }
+
   int new_index = item.type == items_[index].type
                       ? index
                       : ValidateInsertionIndex(item.type, index);
 
   ShelfItem old_item(items_[index]);
   items_[index] = item;
   items_[index].id = old_item.id;
   for (auto& observer : observers_)
     observer.ShelfItemChanged(index, old_item);
 
@@ skipping 94 matching lines @@
 
   return index;
 }
 
 void ShelfModel::RemoveShelfItemDelegate(ShelfID id) {
   if (id_to_item_delegate_map_.find(id) != id_to_item_delegate_map_.end())
     id_to_item_delegate_map_.erase(id);
 }
 
 }  // namespace ash