2020: add and call Fragment::build_display_list

components/layout_2020/flow/root.rs

@@ -6,7 +6,7 @@ use crate::dom_traversal::{Contents, NodeExt};
 use crate::flow::construct::ContainsFloats;
 use crate::flow::float::FloatBox;
 use crate::flow::{BlockContainer, BlockFormattingContext, BlockLevelBox};
-use crate::fragments::Fragment;
+use crate::fragments::{Fragment, IsContentful};
 use crate::geom;
 use crate::geom::flow_relative::Vec2;
 use crate::positioned::AbsolutelyPositionedBox;
@@ -21,6 +21,7 @@ use style::context::SharedStyleContext;
 use style::properties::ComputedValues;
 use style::values::computed::{Length, LengthOrAuto};
 use style_traits::CSSPixel;
+use webrender_api::DisplayListBuilder;
 
 pub struct BoxTreeRoot(BlockFormattingContext);
 pub struct FragmentTreeRoot(Vec<Fragment>);
@@ -129,3 +130,13 @@ impl BoxTreeRoot {
         FragmentTreeRoot(flow_children.fragments)
     }
 }
+
+impl FragmentTreeRoot {
+    pub fn build_display_list(&self, builder: &mut DisplayListBuilder) -> IsContentful {
+        let mut is_contentful = IsContentful(false);
+        for fragment in &self.0 {
+            fragment.build_display_list(builder, &mut is_contentful)
+        }
+        is_contentful
+    }
+}

components/layout_2020/fragments.rs

@@ -9,6 +9,7 @@ use servo_arc::Arc;
 use style::properties::ComputedValues;
 use style::values::computed::Length;
 use style::Zero;
+use webrender_api::DisplayListBuilder;
 
 pub(crate) enum Fragment {
     Box(BoxFragment),
@@ -123,3 +124,18 @@ impl CollapsedMargin {
         self.max_positive + self.min_negative
     }
 }
+
+/// Contentful paint, for the purpose of
+/// https://w3c.github.io/paint-timing/#first-contentful-paint
+/// (i.e. the display list contains items of type text,
+/// image, non-white canvas or SVG). Used by metrics.
+pub struct IsContentful(pub bool);
+
+impl Fragment {
+    pub(crate) fn build_display_list(
+        &self,
+        builder: &mut DisplayListBuilder,
+        is_contentful: &mut IsContentful,
+    ) {
+    }
+}