Layout: Implement CSS Grid using taffy (#32619)

* Add layout.grid.enabled pref

Signed-off-by: Nico Burns <nico@nicoburns.com>

* Add taffy dependency

Signed-off-by: Nico Burns <nico@nicoburns.com>

* Import taffy <-> stylo conversion code from taffy_stylo crate

Signed-off-by: Nico Burns <nico@nicoburns.com>

* Add `Grid` variant to DisplayInside

Signed-off-by: Nico Burns <nico@nicoburns.com>

* Implement CSS Grid using Taffy

Signed-off-by: Nico Burns <nico@nicoburns.com>

Import full stylo_taffy crate

Signed-off-by: Nico Burns <nico@nicoburns.com>

Squashed PR feedback changes

Deduplicate is_document_only_whitespace

Signed-off-by: Nico Burns <nico@nicoburns.com>

Import taffy::AvailableSpace

Signed-off-by: Nico Burns <nico@nicoburns.com>

Rename FlexContext to TaffyContainerContext

Signed-off-by: Nico Burns <nico@nicoburns.com>

Eliminate references to flexbox in taffy/layout module

Signed-off-by: Nico Burns <nico@nicoburns.com>

Use constructors for geom types

Signed-off-by: Nico Burns <nico@nicoburns.com>

Remove comment about abspos elements splitting contiguous text runs

Signed-off-by: Nico Burns <nico@nicoburns.com>

Remove reference to flexbox in taffy/construct

Signed-off-by: Nico Burns <nico@nicoburns.com>

Deduplicate construction of flexbox/grid containers

Signed-off-by: Nico Burns <nico@nicoburns.com>

Make anonymous text runs InFlow

Signed-off-by: Nico Burns <nico@nicoburns.com>

Remove commented code

Signed-off-by: Nico Burns <nico@nicoburns.com>

Update comments

Signed-off-by: Nico Burns <nico@nicoburns.com>

Inline/vendor the stylo/taffy interop code

Signed-off-by: Nico Burns <nico@nicoburns.com>

* Update test expectations

Signed-off-by: Nico Burns <nico@nicoburns.com>

* Fix nits from PR review

Signed-off-by: Nico Burns <nico@nicoburns.com>

---------

Signed-off-by: Nico Burns <nico@nicoburns.com>

components/layout_2020/flexbox/mod.rs

@@ -13,13 +13,17 @@ use style::properties::longhands::flex_wrap::computed_value::T as FlexWrap;
 use style::properties::ComputedValues;
 use style::values::computed::{AlignContent, JustifyContent};
 use style::values::specified::align::AlignFlags;
+use style::values::specified::text::TextDecorationLine;
 
 use crate::cell::ArcRefCell;
+use crate::construct_modern::{ModernContainerBuilder, ModernItemKind};
+use crate::context::LayoutContext;
+use crate::dom::{LayoutBox, NodeExt};
+use crate::dom_traversal::{NodeAndStyleInfo, NonReplacedContents};
 use crate::formatting_contexts::IndependentFormattingContext;
 use crate::fragment_tree::BaseFragmentInfo;
 use crate::positioned::AbsolutelyPositionedBox;
 
-mod construct;
 mod geom;
 mod layout;
 
@@ -95,14 +99,45 @@ pub(crate) struct FlexContainer {
 }
 
 impl FlexContainer {
-    pub(crate) fn new(
-        style: &ServoArc<ComputedValues>,
-        children: Vec<ArcRefCell<FlexLevelBox>>,
+    pub fn construct<'dom>(
+        context: &LayoutContext,
+        info: &NodeAndStyleInfo<impl NodeExt<'dom>>,
+        contents: NonReplacedContents,
+        propagated_text_decoration_line: TextDecorationLine,
     ) -> Self {
+        let text_decoration_line =
+            propagated_text_decoration_line | info.style.clone_text_decoration_line();
+
+        let mut builder = ModernContainerBuilder::new(context, info, text_decoration_line);
+        contents.traverse(context, info, &mut builder);
+        let items = builder.finish();
+
+        let children = items
+            .into_iter()
+            .map(|item| {
+                let box_ = match item.kind {
+                    ModernItemKind::InFlow => ArcRefCell::new(FlexLevelBox::FlexItem(
+                        FlexItemBox::new(item.formatting_context),
+                    )),
+                    ModernItemKind::OutOfFlow => {
+                        let abs_pos_box =
+                            ArcRefCell::new(AbsolutelyPositionedBox::new(item.formatting_context));
+                        ArcRefCell::new(FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(abs_pos_box))
+                    },
+                };
+
+                if let Some(box_slot) = item.box_slot {
+                    box_slot.set(LayoutBox::FlexLevel(box_.clone()));
+                }
+
+                box_
+            })
+            .collect();
+
         Self {
             children,
-            style: style.clone(),
-            config: FlexContainerConfig::new(style),
+            style: info.style.clone(),
+            config: FlexContainerConfig::new(&info.style),
         }
     }
 }
@@ -127,6 +162,13 @@ impl std::fmt::Debug for FlexItemBox {
 }
 
 impl FlexItemBox {
+    fn new(independent_formatting_context: IndependentFormattingContext) -> Self {
+        Self {
+            independent_formatting_context,
+            block_content_size_cache: Default::default(),
+        }
+    }
+
     fn style(&self) -> &ServoArc<ComputedValues> {
         self.independent_formatting_context.style()
     }