Auto merge of #26833 - servo:layout-2020-arcrefcell-abspos, r=SimonSapin

Store abspos boxes in a RefCell too

We want to mutate them when lazily computing their content sizes, but they
are behind an Arc for the hoisting infra, so it also needs its own layer
of inner mutability.

1 files changed, 5 insertions, 6 deletions

diff --git a/components/layout_2020/flexbox.rs b/components/layout_2020/flexbox.rs
index c0d852ff47c..32ea3340ff7 100644
--- a/components/layout_2020/flexbox.rs
+++ b/components/layout_2020/flexbox.rs
@@ -15,7 +15,6 @@ use crate::sizing::{BoxContentSizes, ContentSizes, ContentSizesRequest};
 use crate::style_ext::DisplayGeneratingBox;
 use crate::ContainingBlock;
 use rayon::iter::{IntoParallelIterator, ParallelIterator};
-use servo_arc::Arc;
 use std::borrow::Cow;
 use style::values::computed::Length;
 use style::values::specified::text::TextDecorationLine;
@@ -31,7 +30,7 @@ pub(crate) struct FlexContainer {
 #[derive(Debug, Serialize)]
 pub(crate) enum FlexLevelBox {
     FlexItem(IndependentFormattingContext),
-    OutOfFlowAbsolutelyPositionedBox(Arc<AbsolutelyPositionedBox>),
+    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
 }
 
 impl FlexContainer {
@@ -192,14 +191,14 @@ where
                     };
                     let box_ = if info.style.get_box().position.is_absolutely_positioned() {
                         // https://drafts.csswg.org/css-flexbox/#abspos-items
-                        ArcRefCell::new(FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(Arc::new(
-                            AbsolutelyPositionedBox::construct(
+                        ArcRefCell::new(FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(
+                            ArcRefCell::new(AbsolutelyPositionedBox::construct(
                                 self.context,
                                 &info,
                                 display_inside,
                                 contents,
-                            ),
-                        )))
+                            )),
+                        ))
                     } else {
                         ArcRefCell::new(FlexLevelBox::FlexItem(
                             IndependentFormattingContext::construct(