[blink] Perspective layer should be considered fixed-pos container layer

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1595 matching lines @@
 
   scrolling_coordinator->UpdateLayerPositionConstraint(&owning_layer_);
 
   // Page scale is applied as a transform on the root layout view layer. Because
   // the scroll layer is further up in the hierarchy, we need to avoid marking
   // the root layout view layer as a container.
   bool is_container =
       owning_layer_.GetLayoutObject().CanContainFixedPositionObjects() &&
       !owning_layer_.IsRootLayer();
   scrolling_coordinator->SetLayerIsContainerForFixedPositionLayers(
-      graphics_layer_.get(), is_container);
+      child_transform_layer_ ? child_transform_layer_.get()

[chrishtr, 2017/04/24 15:44:22]

Add a comment explaining.

+                             : graphics_layer_.get(),
+      is_container);
 }
 
 void CompositedLayerMapping::UpdateInternalHierarchy() {
   // m_foregroundLayer has to be inserted in the correct order with child
   // layers, so it's not inserted here.
   if (ancestor_clipping_layer_)
     ancestor_clipping_layer_->RemoveAllChildren();
 
   graphics_layer_->RemoveFromParent();
 
@@ skipping 1977 matching lines @@
   } else if (graphics_layer == decoration_outline_layer_.get()) {
     name = "Decoration Layer";
   } else {
     NOTREACHED();
   }
 
   return name;
 }
 
 }  // namespace blink