Revert of [M55] Generalize layer mirroring for phantom windows

ash/wm/window_mirror_view.h

Index: ash/wm/window_mirror_view.h
diff --git a/ash/wm/window_mirror_view.h b/ash/wm/window_mirror_view.h
index 5fabd641ff0e00933d41df7b379b5705224f49f5..85b990cab04d156df8aa7ff422a2379461e419a4 100644
--- a/ash/wm/window_mirror_view.h
+++ b/ash/wm/window_mirror_view.h
@@ -6,14 +6,12 @@
 #define ASH_WM_WINDOW_MIRROR_VIEW_H_
 
 #include <memory>
+#include <vector>
 
 #include "ash/ash_export.h"
 #include "base/macros.h"
 #include "ui/views/view.h"
-
-namespace ui {
-class LayerTreeOwner;
-}
+#include "ui/wm/core/window_util.h"
 
 namespace ash {
 
@@ -21,8 +19,12 @@
 
 namespace wm {
 
-// A view that mirrors the client area of a single window.
-class WindowMirrorView : public views::View {
+class ForwardingLayerDelegate;
+
+// A view that mirrors the client area of a single window. Layers are lifted
+// from the underlying window (which gets new ones in their place). New paint
+// calls, if any, are forwarded to the underlying window.
+class WindowMirrorView : public views::View, public ::wm::LayerDelegateFactory {
  public:
   explicit WindowMirrorView(WmWindowAura* window);
   ~WindowMirrorView() override;
@@ -32,6 +34,10 @@
   void Layout() override;
   bool GetNeedsNotificationWhenVisibleBoundsChange() const override;
   void OnVisibleBoundsChanged() override;
+
+  // ::wm::LayerDelegateFactory:
+  ui::LayerDelegate* CreateDelegate(ui::Layer* new_layer,
+                                    ui::Layer* layer) override;
 
  private:
   void InitLayerOwner();
@@ -51,6 +57,8 @@
   // the first time the view becomes visible.
   std::unique_ptr<ui::LayerTreeOwner> layer_owner_;
 
+  std::vector<std::unique_ptr<ForwardingLayerDelegate>> delegates_;
+
   DISALLOW_COPY_AND_ASSIGN(WindowMirrorView);
 };