mash: Replace ShelfItemDelegate::CanPin with ShelfItem::pinned_by_policy.

ash/common/shelf/shelf_window_watcher_item_delegate.cc

Index: ash/common/shelf/shelf_window_watcher_item_delegate.cc
diff --git a/ash/common/shelf/shelf_window_watcher_item_delegate.cc b/ash/common/shelf/shelf_window_watcher_item_delegate.cc
index 844a3b89bd677b5a4a5aa5645214f3e7ab612845..0738ce567c8cad95f41962068edacc6638cf1faf 100644
--- a/ash/common/shelf/shelf_window_watcher_item_delegate.cc
+++ b/ash/common/shelf/shelf_window_watcher_item_delegate.cc
@@ -64,10 +64,6 @@ ShelfMenuModel* ShelfWindowWatcherItemDelegate::CreateApplicationMenu(
   return nullptr;
 }
 
-bool ShelfWindowWatcherItemDelegate::CanPin() const {
-  return GetShelfItemType(id_) != TYPE_APP_PANEL;
-}
-
 void ShelfWindowWatcherItemDelegate::Close() {
   window_->CloseWidget();
 }