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..9e6e5a5bc627cc35ef9640c5e33bbebe62bdef82 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;
 
@@ -68,12 +68,14 @@ 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) {
  public:
   Layer();
   explicit Layer(LayerType type);
+  explicit Layer(const Layer&);

[sky, 2016/10/13 19:21:33]

The style guide generally frowns on this, especially for such a complex type,
and it isn't really clear what is copied and what isn't. I think it better to
inline what you need in Mirror().

[Dominik Laskowski, 2016/10/13 22:19:39]

It's also called from LayerOwner::RecreateLayer. Would a Layer::Clone be
preferable?

[sky, 2016/10/14 15:18:41]

Yes please.

[Dominik Laskowski, 2016/10/14 19:15:02]

Done.

   ~Layer() override;
 
   // Retrieves the Layer's compositor. The Layer will walk up its parent chain
@@ -294,6 +296,13 @@ 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 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 +312,7 @@ 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 +423,9 @@ 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 +454,9 @@ class COMPOSITOR_EXPORT Layer
   // This layer's children, in bottom-to-top stacking order.
   std::vector<Layer*> children_;
 
+  std::vector<Layer*> mirrors_;  // Not owned.

[sky, 2016/10/13 19:21:33]

std::vector->std::set as you don't need the order.

[Dominik Laskowski, 2016/10/13 22:19:39]

I started with std::unordered_set, but figured std::vector is more appropriate
given that iteration is more frequent than removal/insertion and lookup isn't
needed.

[sky, 2016/10/14 15:18:41]

I like set to convey it's unordered, but ok.

+  bool sync_bounds_ = false;     // Synchronize bounds to mirrors.
+
   gfx::Rect bounds_;
   gfx::Vector2dF subpixel_position_offset_;
 
@@ -523,7 +538,7 @@ class COMPOSITOR_EXPORT Layer
   // or SetTextureMailbox was called.
   gfx::Size frame_size_in_dip_;
 
-  DISALLOW_COPY_AND_ASSIGN(Layer);
+  DISALLOW_ASSIGN(Layer);
 };
 
 }  // namespace ui