Generalize layer mirroring for phantom windows

ui/wm/core/window_util.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_WM_CORE_WINDOW_UTIL_H_
 #define UI_WM_CORE_WINDOW_UTIL_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 44 matching lines @@
 //
 // As a result of this |root| has freshly created layers, meaning the layers
 // have not yet been painted to.
 //
 // When a non null |delegate_factory| is passed, it will be used to
 // create a delegate for an old layer which had its own delegate.
 WM_EXPORT std::unique_ptr<ui::LayerTreeOwner> RecreateLayers(
     ui::LayerOwner* root,
     LayerDelegateFactory* delegate_factory);
 
+// Returns a layer tree that mirrors |root|. Used for live window previews.
+WM_EXPORT std::unique_ptr<ui::LayerTreeOwner> MirrorLayers(
+    ui::LayerOwner* root,
+    LayerDelegateFactory* delegate_factory);
+
 // Convenience functions that get the TransientWindowManager for the window and
 // redirect appropriately. These are preferable to calling functions on
 // TransientWindowManager as they handle the appropriate NULL checks.
 WM_EXPORT aura::Window* GetTransientParent(aura::Window* window);
 WM_EXPORT const aura::Window* GetTransientParent(
     const aura::Window* window);
 WM_EXPORT const std::vector<aura::Window*>& GetTransientChildren(
     const aura::Window* window);
 WM_EXPORT void AddTransientChild(aura::Window* parent, aura::Window* child);
 WM_EXPORT void RemoveTransientChild(aura::Window* parent, aura::Window* child);
 
 // Returns true if |window| has |ancestor| as a transient ancestor. A transient
 // ancestor is found by following the transient parent chain of the window.
 WM_EXPORT bool HasTransientAncestor(const aura::Window* window,
                                     const aura::Window* ancestor);
 
 }  // namespace wm
 
 #endif  // UI_WM_CORE_WINDOW_UTIL_H_