mash: Fix ShelfItem mojo struct; add enums and traits.

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_model_observer.h"
 
@@ skipping 114 matching lines @@
 }
 
 int ShelfModel::GetItemIndexForType(ShelfItemType type) {
   for (size_t i = 0; i < items_.size(); ++i) {
     if (items_[i].type == type)
       return i;
   }
   return -1;
 }
 
-ShelfItems::const_iterator ShelfModel::ItemByID(int id) const {
+ShelfItems::const_iterator ShelfModel::ItemByID(ShelfID id) const {
   for (ShelfItems::const_iterator i = items_.begin(); i != items_.end(); ++i) {
     if (i->id == id)
       return i;
   }
   return items_.end();
 }
 
 int ShelfModel::FirstRunningAppIndex() const {
   ShelfItem weight_dummy;
   weight_dummy.type = TYPE_APP;
@@ skipping 55 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