Disable ERROR logging for the valid case in app list sync service.

chrome/browser/ui/app_list/app_list_syncable_service.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/app_list/app_list_syncable_service.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/macros.h"
@@ skipping 1007 matching lines @@
 
 void AppListSyncableService::ProcessExistingSyncItem(SyncItem* sync_item) {
   if (sync_item->item_type ==
       sync_pb::AppListSpecifics::TYPE_REMOVE_DEFAULT_APP) {
     return;
   }
   VLOG(2) << "ProcessExistingSyncItem: " << sync_item->ToString();
   AppListItem* app_item = model_->FindItem(sync_item->item_id);
   DVLOG(2) << " AppItem: " << app_item->ToDebugString();
   if (!app_item) {
-    LOG(ERROR) << "Item not found in model: " << sync_item->ToString();
+    // This is expected in case the user uses devices with different app set,
+    // for example, ARC enabled and ARC disabled devices. Another scenario is
+    // app pinned by default (YouTube, for instance) but which has not been yet
+    // installed on this device.
+    DVLOG(2) << "Skip updating missing item : " << sync_item->ToString();
     return;
   }
   // This is the only place where sync can cause an item to change folders.
   if (app_list::switches::IsFolderUIEnabled() &&
       app_item->folder_id() != sync_item->parent_id &&
       !AppIsOem(app_item->id())) {
     VLOG(2) << " Moving Item To Folder: " << sync_item->parent_id;
     model_->MoveItemToFolder(app_item, sync_item->parent_id);
   }
   UpdateAppItemFromSyncItem(sync_item, app_item);
@@ skipping 207 matching lines @@
     res += " { " + item_name + " }";
     res += " [" + item_ordinal.ToDebugString() + "]";
     if (!parent_id.empty())
       res += " <" + parent_id.substr(0, 8) + ">";
     res += " [" + item_pin_ordinal.ToDebugString() + "]";
   }
   return res;
 }
 
 }  // namespace app_list