Remove the HasOwnBackingButPaintsIntoAncestor compositing state.

Source/core/rendering/compositing/CompositingLayerAssigner.cpp

Index: Source/core/rendering/compositing/CompositingLayerAssigner.cpp
diff --git a/Source/core/rendering/compositing/CompositingLayerAssigner.cpp b/Source/core/rendering/compositing/CompositingLayerAssigner.cpp
index e95e56edde1a7f4402e91e6a8ff2529a09f3414b..44727edf222c79faa5fc90060f6f76b9bf2608f8 100644
--- a/Source/core/rendering/compositing/CompositingLayerAssigner.cpp
+++ b/Source/core/rendering/compositing/CompositingLayerAssigner.cpp
@@ -275,8 +275,8 @@ void CompositingLayerAssigner::assignLayersToBackingsInternal(RenderLayer* layer
     }
 
     if (m_layerSquashingEnabled) {
-        // At this point, if the layer is to be "separately" composited, then its backing becomes the most recent in paint-order.
-        if (layer->compositingState() == PaintsIntoOwnBacking || layer->compositingState() == HasOwnBackingButPaintsIntoAncestor) {
+        // At this point, if the layer is to be separately composited, then its backing becomes the most recent in paint-order.
+        if (layer->compositingState() == PaintsIntoOwnBacking) {
             ASSERT(!requiresSquashing(layer->compositingReasons()));
             squashingState.updateSquashingStateForNewMapping(layer->compositedLayerMapping(), layer->hasCompositedLayerMapping());
         }