Handle nested position:sticky elements correctly (compositor)

cc/blink/web_layer_impl.cc

Index: cc/blink/web_layer_impl.cc
diff --git a/cc/blink/web_layer_impl.cc b/cc/blink/web_layer_impl.cc
index ff07c7c0b1fdd073f0fb9588bd2f7fdfdcdacdef..6e6d7f6a8c7fb8d7a63881f97ac8d5a0eb8cc513 100644
--- a/cc/blink/web_layer_impl.cc
+++ b/cc/blink/web_layer_impl.cc
@@ -378,6 +378,10 @@ ToWebLayerStickyPositionConstraint(
       constraint.scroll_container_relative_sticky_box_rect;
   web_constraint.scrollContainerRelativeContainingBlockRect =
       constraint.scroll_container_relative_containing_block_rect;
+  web_constraint.nearestLayerShiftingStickyBox =
+      constraint.nearest_layer_shifting_sticky_box;
+  web_constraint.nearestLayerShiftingContainingBlock =
+      constraint.nearest_layer_shifting_containing_block;
   return web_constraint;
 }
 static cc::LayerStickyPositionConstraint ToStickyPositionConstraint(
@@ -398,6 +402,10 @@ static cc::LayerStickyPositionConstraint ToStickyPositionConstraint(
       web_constraint.scrollContainerRelativeStickyBoxRect;
   constraint.scroll_container_relative_containing_block_rect =
       web_constraint.scrollContainerRelativeContainingBlockRect;
+  constraint.nearest_layer_shifting_sticky_box =
+      web_constraint.nearestLayerShiftingStickyBox;
+  constraint.nearest_layer_shifting_containing_block =
+      web_constraint.nearestLayerShiftingContainingBlock;

[chrishtr, 2017/03/21 22:18:28]

This seems unused.

[smcgruer, 2017/03/21 22:41:35]

It is used. See property_tree_builder.cc line 787, where this is used to
calculate nearest_node_shifting_containing_block, which is then used to get the
ancestor total to adjust the constraint rect.

[chrishtr, 2017/03/21 23:26:05]

I see, sorry.

It seems weird to me to expose a "containing block" name to cc. cc shouldn't
have to care about
containing blocks. More comments below.

   return constraint;
 }
 void WebLayerImpl::setStickyPositionConstraint(