layout: Store `Fragment` results in `LayoutBoxBase` and start using them for queries (#36583)

Start storing a link to laid-out `Fragment`s in `LayoutBoxBase`, so that
these are accessible for queries and eventually for incremental layout.
Some box tree data structures lacked a `LayoutBoxBase`, such as table
tracks and table track groups[^1].

In addition, start using these `Fragment`s for queries instead of
walking the entire `Fragment` tree. Currently, this isn't possible for
most queries as `Fragment`s do not cache their absolute offsets (which
are often necessary). This change uses the new box tree `Fragment`s for
most resolved style queries.

[^1]: Note that only rows and row groups store `Fragment`s as columsn
and
   colgroups do not produce any.

Testing: This is covered by existing tests.
Fixes: This is part of #36525.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/components/layout_2020/layout_box_base.rs b/components/layout_2020/layout_box_base.rs
index 8a88a5855dc..54f7575391c 100644
--- a/components/layout_2020/layout_box_base.rs
+++ b/components/layout_2020/layout_box_base.rs
@@ -29,6 +29,7 @@ pub(crate) struct LayoutBoxBase {
     pub cached_inline_content_size:
         AtomicRefCell<Option<Box<(SizeConstraint, InlineContentSizesResult)>>>,
     pub cached_layout_result: AtomicRefCell<Option<Box<CacheableLayoutResultAndInputs>>>,
+    pub fragments: AtomicRefCell<Vec<Fragment>>,
 }
 
 impl LayoutBoxBase {
@@ -38,6 +39,7 @@ impl LayoutBoxBase {
             style,
             cached_inline_content_size: AtomicRefCell::default(),
             cached_layout_result: AtomicRefCell::default(),
+            fragments: AtomicRefCell::default(),
         }
     }
 
@@ -69,6 +71,22 @@ impl LayoutBoxBase {
     pub(crate) fn invalidate_cached_fragment(&self) {
         let _ = self.cached_layout_result.borrow_mut().take();
     }
+
+    pub(crate) fn fragments(&self) -> Vec<Fragment> {
+        self.fragments.borrow().clone()
+    }
+
+    pub(crate) fn add_fragment(&self, fragment: Fragment) {
+        self.fragments.borrow_mut().push(fragment);
+    }
+
+    pub(crate) fn set_fragment(&self, fragment: Fragment) {
+        *self.fragments.borrow_mut() = vec![fragment];
+    }
+
+    pub(crate) fn clear_fragments(&self) {
+        self.fragments.borrow_mut().clear();
+    }
 }
 
 impl Debug for LayoutBoxBase {