Generalize layer mirroring for phantom windows

ui/wm/core/window_util.cc

Index: ui/wm/core/window_util.cc
diff --git a/ui/wm/core/window_util.cc b/ui/wm/core/window_util.cc
index 0dc44d50da993b8a289b2f4ce15f04b240662d9c..a4244bdbb1f42e3dc932cc114c5d9872d8715317 100644
--- a/ui/wm/core/window_util.cc
+++ b/ui/wm/core/window_util.cc
@@ -4,6 +4,7 @@
 
 #include "ui/wm/core/window_util.h"
 
+#include "base/memory/ptr_util.h"
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_tree_owner.h"
@@ -37,6 +38,24 @@ void CloneChildren(ui::Layer* to_clone,
   }
 }
 
+// Invokes Mirror() on all the children of |to_mirror|, adding the newly cloned
+// children to |parent|.
+//
+// WARNING: It is assumed that |parent| is ultimately owned by a LayerTreeOwner.
+void MirrorChildren(ui::Layer* to_mirror,
+                    ui::Layer* parent,
+                    wm::LayerDelegateFactory* factory,
+                    bool sync_bounds) {
+  for (auto* child : to_mirror->children()) {
+    child->set_sync_bounds(sync_bounds);
+    ui::Layer* mirror = child->Mirror().release();
+    if (factory && child->delegate())
+      mirror->set_delegate(factory->CreateDelegate(mirror, child));
+    parent->Add(mirror);
+    MirrorChildren(child, mirror, factory, sync_bounds);
+  }
+}
+
 }  // namespace
 
 namespace wm {
@@ -88,8 +107,7 @@ aura::Window* GetToplevelWindow(aura::Window* window) {
 std::unique_ptr<ui::LayerTreeOwner> RecreateLayers(
     ui::LayerOwner* root,
     LayerDelegateFactory* factory) {
-  std::unique_ptr<ui::LayerTreeOwner> old_layer(
-      new ui::LayerTreeOwner(root->RecreateLayer().release()));
+  auto old_layer = base::MakeUnique<ui::LayerTreeOwner>(root->RecreateLayer());
   if (old_layer->root()) {
     if (factory) {
       old_layer->root()->set_delegate(
@@ -100,6 +118,19 @@ std::unique_ptr<ui::LayerTreeOwner> RecreateLayers(
   return old_layer;
 }
 
+std::unique_ptr<ui::LayerTreeOwner> MirrorLayers(
+    ui::LayerOwner* root,
+    LayerDelegateFactory* factory,
+    bool sync_bounds) {
+  auto mirror = base::MakeUnique<ui::LayerTreeOwner>(root->layer()->Mirror());
+  if (factory) {
+    mirror->root()->set_delegate(
+        factory->CreateDelegate(mirror->root(), root->layer()));
+  }
+  MirrorChildren(root->layer(), mirror->root(), factory, sync_bounds);
+  return mirror;
+}
+
 aura::Window* GetTransientParent(aura::Window* window) {
   return const_cast<aura::Window*>(GetTransientParent(
                                  const_cast<const aura::Window*>(window)));