Handle nested position:sticky elements

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 43d7caa7f202b524f31c1b004f3600d19d70183b..d92a7285a42665b9451139d18495d1c581ce0ab7 100644
--- a/cc/blink/web_layer_impl.cc
+++ b/cc/blink/web_layer_impl.cc
@@ -378,6 +378,9 @@ ToWebLayerStickyPositionConstraint(
       constraint.scroll_container_relative_sticky_box_rect;
   web_constraint.scrollContainerRelativeContainingBlockRect =
       constraint.scroll_container_relative_containing_block_rect;
+  // TODO(smcgruer): Copy over ancestor pointers too.
+  web_constraint.cachedComputedStickyOffset =
+      blink::WebFloatSize(constraint.cached_computed_sticky_offset);
   return web_constraint;
 }
 static cc::LayerStickyPositionConstraint ToStickyPositionConstraint(
@@ -398,6 +401,16 @@ 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
+          ? web_constraint.nearestLayerShiftingStickyBox->ccLayer()
+          : nullptr;
+  constraint.nearest_layer_shifting_containing_block =
+      web_constraint.nearestLayerShiftingContainingBlock
+          ? web_constraint.nearestLayerShiftingContainingBlock->ccLayer()
+          : nullptr;
+  constraint.cached_computed_sticky_offset =
+      web_constraint.cachedComputedStickyOffset;
   return constraint;
 }
 void WebLayerImpl::setStickyPositionConstraint(