[ash-md] Keeps overview mode shield above DesktopBackgroundView

ash/desktop_background/desktop_background_view.cc

Index: ash/desktop_background/desktop_background_view.cc
diff --git a/ash/desktop_background/desktop_background_view.cc b/ash/desktop_background/desktop_background_view.cc
index be85e5e6c455a2eee9371ae8a9dff93a4aca2cc5..adbd066f688590ef34d23bbb7094df72890a2867 100644
--- a/ash/desktop_background/desktop_background_view.cc
+++ b/ash/desktop_background/desktop_background_view.cc
@@ -41,6 +41,9 @@ class LayerControlView : public views::View {
   // Overrides views::View.
   void Layout() override {
     WmWindow* window = WmLookup::Get()->GetWindowForWidget(GetWidget());
+    // Keep |this| at the bottom since there may be other windows on top of the
+    // background view such as an overview mode shield.
+    window->GetParent()->StackChildAtBottom(window);
     display::Display display = window->GetDisplayNearestWindow();
     DisplayInfo info = WmShell::Get()->GetDisplayInfo(display.id());
     float ui_scale = info.GetEffectiveUIScale();