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

ash/shell/window_watcher_shelf_item_delegate.cc

Index: ash/shell/window_watcher_shelf_item_delegate.cc
diff --git a/ash/shell/window_watcher_shelf_item_delegate.cc b/ash/shell/window_watcher_shelf_item_delegate.cc
index 1a73dea7696f9881558e4010186d9baee3d86644..6c45e0971b61ff4009dafc2b6986aa5e74ec3f65 100644
--- a/ash/shell/window_watcher_shelf_item_delegate.cc
+++ b/ash/shell/window_watcher_shelf_item_delegate.cc
@@ -40,10 +40,6 @@ ShelfMenuModel* WindowWatcherShelfItemDelegate::CreateApplicationMenu(
   return nullptr;
 }
 
-bool WindowWatcherShelfItemDelegate::CanPin() const {
-  return true;
-}
-
 void WindowWatcherShelfItemDelegate::Close() {}
 
 }  // namespace shell