[M55] Generalize layer mirroring for phantom windows

ash/utility/screenshot_controller.cc

Index: ash/utility/screenshot_controller.cc
diff --git a/ash/utility/screenshot_controller.cc b/ash/utility/screenshot_controller.cc
index 64e4f99785f09fd729063fb9d05434708c248969..d51a388232ea5fa6a8259ad35fd7da930e33a325 100644
--- a/ash/utility/screenshot_controller.cc
+++ b/ash/utility/screenshot_controller.cc
@@ -88,7 +88,7 @@ class ScreenshotController::ScreenshotLayer : public ui::LayerOwner,
  public:
   ScreenshotLayer(ui::Layer* parent, bool immediate_overlay)
       : draw_inactive_overlay_(immediate_overlay) {
-    SetLayer(new ui::Layer(ui::LAYER_TEXTURED));
+    SetLayer(base::MakeUnique<ui::Layer>(ui::LAYER_TEXTURED));
     layer()->SetFillsBoundsOpaquely(false);
     layer()->SetBounds(parent->bounds());
     parent->Add(layer());