Make hotseat widget layer not drawn

BUG=1021773

Change-Id: I10b0f70f41f5c067049757ec093424c5a8641d84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2070689
Commit-Queue: Toni Baržić <tbarzic@chromium.org>
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Auto-Submit: Toni Baržić <tbarzic@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744081}

ash/shelf/hotseat_widget.cc

@@ -294,6 +294,7 @@ void HotseatWidget::Initialize(aura::Window* container, Shelf* shelf) {
   params.opacity = views::Widget::InitParams::WindowOpacity::kTranslucent;
   params.ownership = views::Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;
   params.parent = container;
+  params.layer_type = ui::LAYER_NOT_DRAWN;
   Init(std::move(params));
   set_focus_on_creation(false);
   GetFocusManager()->set_arrow_key_traversal_enabled_for_widget(true);