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

chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.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 "chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl.h"
 
 #include <stddef.h>
 
 #include <vector>
 
@@ skipping 1368 matching lines @@
     TabStripModel* tab_strip = browser_to_close.back()->tab_strip_model();
     if (!tab_strip->empty())
       tab_strip->CloseWebContentsAt(0, TabStripModel::CLOSE_NONE);
     browser_to_close.pop_back();
   }
 }
 
 void ChromeLauncherControllerImpl::SetShelfItemDelegate(
     ash::ShelfID id,
     ash::mojom::ShelfItemDelegate* item_delegate) {
-  DCHECK_GT(id, 0);
+  DCHECK_NE(id, ash::kInvalidShelfID);
   DCHECK(item_delegate);
   model_->SetShelfItemDelegate(
       id, base::WrapUnique<ash::mojom::ShelfItemDelegate>(item_delegate));
 }
 
 void ChromeLauncherControllerImpl::ReleaseProfile() {
   if (app_sync_ui_state_)
     app_sync_ui_state_->RemoveObserver(this);
 
   app_updaters_.clear();
@@ skipping 99 matching lines @@
     LauncherItemController* controller = GetLauncherItemController(item.id);
     if (!controller || controller->image_set_by_controller())
       continue;
     item.image = image;
     if (arc_deferred_launcher_)
       arc_deferred_launcher_->MaybeApplySpinningEffect(id, &item.image);
     model_->Set(index, item);
     // It's possible we're waiting on more than one item, so don't break.
   }
 }