Remove the HasOwnBackingButPaintsIntoAncestor compositing state.

Source/core/rendering/compositing/CompositingState.h

Index: Source/core/rendering/compositing/CompositingState.h
diff --git a/Source/core/rendering/compositing/CompositingState.h b/Source/core/rendering/compositing/CompositingState.h
index 9e2cb4be95a4a467b98db5c45b5fe683c4b6c24d..2601aacf4900c7d7e9f84b65b6ab7371254d5d97 100644
--- a/Source/core/rendering/compositing/CompositingState.h
+++ b/Source/core/rendering/compositing/CompositingState.h
@@ -11,12 +11,6 @@ enum CompositingState {
     // The layer paints into its enclosing composited ancestor.
     NotComposited = 0,
 
-    // The layer is composited, but its contents still paint into enclosing composited ancestor.
-    // In this state, paint invalidations must be sent to the enclosing composited ancestor.
-    // Typically this happens when a layer's properties need to be represented in the compositor
-    // output data structures, but it doesn't actually have any other reasons to be composited.
-    HasOwnBackingButPaintsIntoAncestor = 1,
-
     PaintsIntoOwnBacking = 2,
 
     // In this state, the RenderLayer subtree paints into a backing that is shared by