Generalize layer mirroring for phantom windows

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index 7c7e4e32562c1899c69a438587c10cc6aaeafea6..a33b21cc082451e7f5f96aaa0fc16429faf41ec6 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -28,6 +28,7 @@
 #include "ui/compositor/compositor.h"
 #include "ui/compositor/layer_animation_delegate.h"
 #include "ui/compositor/layer_delegate.h"
+#include "ui/compositor/layer_observer.h"
 #include "ui/compositor/layer_type.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/image/image_skia.h"
@@ -52,7 +53,6 @@ namespace ui {
 
 class Compositor;
 class LayerAnimator;
-class LayerObserver;
 class LayerOwner;
 class LayerThreadedAnimationDelegate;
 
@@ -68,6 +68,7 @@ class LayerThreadedAnimationDelegate;
 // NULL, but the children are not deleted.
 class COMPOSITOR_EXPORT Layer
     : public LayerAnimationDelegate,
+      public LayerObserver,
       NON_EXPORTED_BASE(public cc::ContentLayerClient),
       NON_EXPORTED_BASE(public cc::TextureLayerClient),
       NON_EXPORTED_BASE(public cc::LayerClient) {
@@ -76,6 +77,9 @@ class COMPOSITOR_EXPORT Layer
   explicit Layer(LayerType type);
   ~Layer() override;
 
+  // Note that only solid color and surface content is copied.
+  std::unique_ptr<Layer> Clone() const;
+
   // Retrieves the Layer's compositor. The Layer will walk up its parent chain
   // to locate it. Returns NULL if the Layer is not attached to a compositor.
   Compositor* GetCompositor() {
@@ -294,6 +298,13 @@ class COMPOSITOR_EXPORT Layer
                       float scale,
                       gfx::Size frame_size_in_dip);
 
+  // Returns a new layer that mirrors this layer and is optionally synchronized
+  // with the bounds thereof. Note that children are not mirrored, and that the
+  // content is only mirrored if painted by a delegate or backed by a surface.
+  std::unique_ptr<Layer> Mirror();
+
+  void set_sync_bounds(bool sync_bounds) { sync_bounds_ = sync_bounds; }
+
   bool has_external_content() {
     return texture_layer_.get() || surface_layer_.get();
   }
@@ -303,7 +314,7 @@ class COMPOSITOR_EXPORT Layer
 
   // Sets the layer's fill color.  May only be called for LAYER_SOLID_COLOR.
   void SetColor(SkColor color);
-  SkColor GetTargetColor();
+  SkColor GetTargetColor() const;
   SkColor background_color() const;
 
   // Updates the nine patch layer's image, aperture and border. May only be
@@ -414,6 +425,9 @@ class COMPOSITOR_EXPORT Layer
   LayerThreadedAnimationDelegate* GetThreadedAnimationDelegate() override;
   LayerAnimatorCollection* GetLayerAnimatorCollection() override;
 
+  // LayerObserver:
+  void LayerDestroyed(Layer* layer) override;
+
   // Creates a corresponding composited layer for |type_|.
   void CreateCcLayer();
 
@@ -442,6 +456,12 @@ class COMPOSITOR_EXPORT Layer
   // This layer's children, in bottom-to-top stacking order.
   std::vector<Layer*> children_;
 
+  class LayerMirror;
+  std::vector<std::unique_ptr<LayerMirror>> mirrors_;
+
+  // If true, changes to the bounds of this layer are propagated to mirrors.
+  bool sync_bounds_ = false;
+
   gfx::Rect bounds_;
   gfx::Vector2dF subpixel_position_offset_;