Implements core logic for Pixel Canvas

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index 7feab9bbd4bb11d53998ee4fa24e69a68488a7b3..6c3c7eeee7b402593513529d2449b5c53ee7f1f1 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -418,6 +418,11 @@ class COMPOSITOR_EXPORT Layer
     return frame_size_in_dip_;
   }
 
+  // The back link from the mask layer to it's associated masked layer.
+  // We keep this reference for the case that if the mask layer gets deleted
+  // while attached to the main layer before the main layer is deleted.
+  const Layer* layer_mask_back_link() const { return layer_mask_back_link_; }
+
  private:
   friend class LayerOwner;
   class LayerMirror;