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 7c1ab4bf4a42e5755ee6031de1bcd3451a29dbb0..b4d8f96b8c50d0b784c1b697881e2a5a56fc5a74 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -415,6 +415,11 @@ 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;