Ensure PaintArtifactCompositor assigns a scroll tree index to all cc layers

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/graphics/compositing/PaintArtifactCompositor.h"
 
 #include "cc/layers/content_layer_client.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/picture_layer.h"
 #include "cc/playback/compositing_display_item.h"
@@ skipping 705 matching lines @@
 
     layer->set_offset_to_transform_parent(layerOffset);
     layer->SetElementId(pendingLayer.propertyTreeState.compositorElementId());
 
     m_rootLayer->AddChild(layer);
     layer->set_property_tree_sequence_number(
         PropertyTreeManager::kPropertyTreeSequenceNumber);
     layer->SetTransformTreeIndex(transformId);
     layer->SetClipTreeIndex(clipId);
     layer->SetEffectTreeIndex(effectId);
-    if (const auto* scrollNode = transform->scrollNode()) {
-      layer->SetScrollTreeIndex(
-          propertyTreeManager.ensureCompositorScrollNode(scrollNode));
-    }
+    layer->SetScrollTreeIndex(propertyTreeManager.ensureCompositorScrollNode(
+        transform->findEnclosingScrollNode()));
 
     layer->SetShouldCheckBackfaceVisibility(pendingLayer.backfaceHidden);
 
     if (m_extraDataForTestingEnabled)
       m_extraDataForTesting->contentLayers.push_back(layer);
   }
   m_contentLayerClients.clear();
   m_contentLayerClients.swap(newContentLayerClients);
 
   // Mark the property trees as having been rebuilt.
   layerTreeHost->property_trees()->sequence_number =
       PropertyTreeManager::kPropertyTreeSequenceNumber;
   layerTreeHost->property_trees()->needs_rebuild = false;
   layerTreeHost->property_trees()->ResetCachedData();
 }
 
 #ifndef NDEBUG
 void PaintArtifactCompositor::showDebugData() {
   LOG(ERROR) << layersAsJSON(LayerTreeIncludesDebugInfo)
                     ->toPrettyJSONString()
                     .utf8()
                     .data();
 }
 #endif
 
 }  // namespace blink