Unify the calculation of main thread offset of sticky element

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 5526a70f430a682daf21468d400d99c8d8efd263..ca4db743f8d777cec6e8e50130ca8c24dbbb864d 100644
--- a/cc/blink/web_layer_impl.cc
+++ b/cc/blink/web_layer_impl.cc
@@ -375,8 +375,6 @@ ToWebLayerStickyPositionConstraint(
   web_constraint.right_offset = constraint.right_offset;
   web_constraint.top_offset = constraint.top_offset;
   web_constraint.bottom_offset = constraint.bottom_offset;
-  web_constraint.parent_relative_sticky_box_offset =
-      constraint.parent_relative_sticky_box_offset;
   web_constraint.scroll_container_relative_sticky_box_rect =
       constraint.scroll_container_relative_sticky_box_rect;
   web_constraint.scroll_container_relative_containing_block_rect =
@@ -399,8 +397,6 @@ static cc::LayerStickyPositionConstraint ToStickyPositionConstraint(
   constraint.right_offset = web_constraint.right_offset;
   constraint.top_offset = web_constraint.top_offset;
   constraint.bottom_offset = web_constraint.bottom_offset;
-  constraint.parent_relative_sticky_box_offset =
-      web_constraint.parent_relative_sticky_box_offset;
   constraint.scroll_container_relative_sticky_box_rect =
       web_constraint.scroll_container_relative_sticky_box_rect;
   constraint.scroll_container_relative_containing_block_rect =
@@ -421,6 +417,14 @@ blink::WebLayerStickyPositionConstraint WebLayerImpl::StickyPositionConstraint()
       layer_->sticky_position_constraint());
 }
 
+void WebLayerImpl::SetStickyMainThreadOffset(const blink::WebSize& offset) {
+  layer_->SetStickyMainThreadOffset(offset);
+}
+
+blink::WebSize WebLayerImpl::StickyMainThreadOffset() const {
+  return layer_->sticky_main_thread_offset();
+}
+
 void WebLayerImpl::SetScrollClient(blink::WebLayerScrollClient* scroll_client) {
   if (scroll_client) {
     layer_->set_did_scroll_callback(