layout: Measure stacking context tree in layout thread memory report (#38762)

Measures the memory usage of the stacking context tree in the memory
report of the layout thread by adding `MallocSizeOf` to
`StackingContextTree` and all the types required for that. Also requires
adding `MallocSizeOf` to some webrender types.

Testing: Manually looked at about:memory
<img width="636" height="241" alt="image"
src="https://github.com/user-attachments/assets/6bf9d65a-0bf0-4a99-99b5-ddedba3269c1"
/>

Fixes: https://github.com/servo/servo/issues/38725

---------

Signed-off-by: Rahul Menon <menonrahul02@gmail.com>

components/layout/display_list/clip.rs

@@ -4,6 +4,7 @@
 
 use app_units::Au;
 use base::id::ScrollTreeNodeId;
+use malloc_size_of_derive::MallocSizeOf;
 use style::values::computed::basic_shape::{BasicShape, ClipPath};
 use style::values::computed::length_percentage::NonNegativeLengthPercentage;
 use style::values::computed::position::Position;
@@ -16,7 +17,7 @@ use super::{BuilderForBoxFragment, compute_margin_box_radius, normalize_radii};
 
 /// An identifier for a clip used during StackingContextTree construction. This is a simple index in
 /// a [`ClipStore`]s vector of clips.
-#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, PartialEq)]
 pub(crate) struct ClipId(pub usize);
 
 impl ClipId {
@@ -27,7 +28,7 @@ impl ClipId {
 /// All the information needed to create a clip on a WebRender display list. These are created at
 /// two times: during `StackingContextTree` creation and during WebRender display list construction.
 /// Only the former are stored in a [`ClipStore`].
-#[derive(Clone)]
+#[derive(Clone, MallocSizeOf)]
 pub(crate) struct Clip {
     pub id: ClipId,
     pub radii: BorderRadius,
@@ -39,7 +40,7 @@ pub(crate) struct Clip {
 /// A simple vector of [`Clip`] that is built during `StackingContextTree` construction.
 /// These are later turned into WebRender clips and clip chains during WebRender display
 /// list construction.
-#[derive(Clone, Default)]
+#[derive(Clone, Default, MallocSizeOf)]
 pub(crate) struct StackingContextTreeClipStore(pub Vec<Clip>);
 
 impl StackingContextTreeClipStore {

components/layout/display_list/stacking_context.rs

@@ -18,6 +18,7 @@ use embedder_traits::ViewportDetails;
 use euclid::SideOffsets2D;
 use euclid::default::{Point2D, Rect, Size2D};
 use log::warn;
+use malloc_size_of_derive::MallocSizeOf;
 use servo_config::opts::DebugOptions;
 use style::Zero;
 use style::color::AbsoluteColor;
@@ -92,7 +93,7 @@ impl ContainingBlock {
 
 pub(crate) type ContainingBlockInfo<'a> = ContainingBlockManager<'a, ContainingBlock>;
 
-#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
+#[derive(Clone, Copy, Debug, Eq, Ord, MallocSizeOf, PartialEq, PartialOrd)]
 pub(crate) enum StackingContextSection {
     OwnBackgroundsAndBorders,
     DescendantBackgroundsAndBorders,
@@ -100,6 +101,7 @@ pub(crate) enum StackingContextSection {
     Outline,
 }
 
+#[derive(MallocSizeOf)]
 pub(crate) struct ScrollFrameHitTestItem {
     /// The [`ScrollTreeNodeId`] of the spatial node that contains this hit test item.
     pub scroll_node_id: ScrollTreeNodeId,
@@ -116,6 +118,7 @@ pub(crate) struct ScrollFrameHitTestItem {
     pub external_scroll_id: ExternalScrollId,
 }
 
+#[derive(MallocSizeOf)]
 pub(crate) struct StackingContextTree {
     /// The root stacking context of this [`StackingContextTree`].
     pub root_stacking_context: StackingContext,
@@ -282,7 +285,7 @@ impl StackingContextTree {
 }
 
 /// The text decorations for a Fragment, collecting during [`StackingContextTree`] construction.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, MallocSizeOf)]
 pub(crate) struct FragmentTextDecoration {
     pub line: TextDecorationLine,
     pub color: AbsoluteColor,
@@ -293,6 +296,7 @@ pub(crate) struct FragmentTextDecoration {
 ///
 /// This is generally part of a fragment, like its borders or foreground, but it
 /// can also be a stacking container that needs to be painted in fragment order.
+#[derive(MallocSizeOf)]
 pub(crate) enum StackingContextContent {
     /// A fragment that does not generate a stacking context or stacking container.
     Fragment {
@@ -303,6 +307,7 @@ pub(crate) enum StackingContextContent {
         containing_block: PhysicalRect<Au>,
         fragment: Fragment,
         is_collapsed_table_borders: bool,
+        #[conditional_malloc_size_of]
         text_decorations: Arc<Vec<FragmentTextDecoration>>,
     },
 
@@ -354,7 +359,7 @@ impl StackingContextContent {
     }
 }
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq)]
 pub(crate) enum StackingContextType {
     RealStackingContext,
     PositionedStackingContainer,
@@ -367,6 +372,7 @@ pub(crate) enum StackingContextType {
 ///
 /// We use the term “real stacking context” in situations that call for a
 /// stacking context but not a stacking container.
+#[derive(MallocSizeOf)]
 pub struct StackingContext {
     /// The spatial id of this fragment. This is used to properly handle
     /// things like preserve-3d.
@@ -416,14 +422,14 @@ pub struct StackingContext {
 }
 
 /// Refers to one of the child contents or stacking contexts of a [StackingContext].
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, MallocSizeOf)]
 pub struct DebugPrintItem {
     field: DebugPrintField,
     index: usize,
 }
 
 /// Refers to one of the vecs of a [StackingContext].
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, MallocSizeOf)]
 pub enum DebugPrintField {
     Contents,
     RealStackingContextsAndPositionedStackingContainers,