Remove Ash shelf dimmer.

ash/common/shelf/shelf_view.cc

Index: ash/common/shelf/shelf_view.cc
diff --git a/ash/common/shelf/shelf_view.cc b/ash/common/shelf/shelf_view.cc
index 74cc4bc1d4becf8fbfdfc9ca51045e65afdcc672..2adbf2382d33ae4636d223a44a6691610536f751 100644
--- a/ash/common/shelf/shelf_view.cc
+++ b/ash/common/shelf/shelf_view.cc
@@ -1843,7 +1843,6 @@ void ShelfView::ShowMenu(std::unique_ptr<ui::MenuModel> menu_model,
     }
   }
 
-  shelf_widget_->ForceUndimming(true);
   // NOTE: if you convert to HAS_MNEMONICS be sure to update menu building code.
   launcher_menu_runner_->RunMenuAt(source->GetWidget(), nullptr, anchor,
                                    menu_alignment, source_type);
@@ -1851,7 +1850,6 @@ void ShelfView::ShowMenu(std::unique_ptr<ui::MenuModel> menu_model,
 
 void ShelfView::OnMenuClosed(views::InkDrop* ink_drop) {
   context_menu_id_ = 0;
-  shelf_widget_->ForceUndimming(false);
 
   // Hide the hide overflow bubble after showing a context menu for its items.
   if (owner_overflow_bubble_)