compositor: Do not allow script to scroll beyond node boundaries (#37412)

The compositor was accepting scroll offsets from the ScriptThread
without checking their boundaries. In some cases this could cause a
temporary discrepancy with the rendered scroll offset. This change makes
it so that all offset updates for scroll ayers in the compositor do not
scroll past the scroll boundaries of the node.

Testing: Two new tests pass with this change:
 - `/css/css-position/sticky/position-sticky-left-003.html`
 -  `/css/css-position/sticky/position-sticky-top-003.html`

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/compositing/compositor.rs

@@ -15,7 +15,9 @@ use base::cross_process_instant::CrossProcessInstant;
 use base::id::{PipelineId, WebViewId};
 use base::{Epoch, WebRenderEpochToU16};
 use bitflags::bitflags;
-use compositing_traits::display_list::{CompositorDisplayListInfo, HitTestInfo, ScrollTree};
+use compositing_traits::display_list::{
+    CompositorDisplayListInfo, HitTestInfo, ScrollTree, ScrollType,
+};
 use compositing_traits::rendering_context::RenderingContext;
 use compositing_traits::{
     CompositionPipeline, CompositorMsg, ImageUpdate, SendableFrameTree, WebViewTrait,
@@ -738,22 +740,22 @@ impl IOCompositor {
                 };
 
                 let offset = LayoutVector2D::new(point.x, point.y);
-                if !pipeline_details
+                let Some(offset) = pipeline_details
                     .scroll_tree
                     .set_scroll_offsets_for_node_with_external_scroll_id(
                         external_scroll_id,
                         -offset,
+                        ScrollType::Script,
                     )
-                {
-                    warn!("Could not scroll not with id: {external_scroll_id:?}");
+                else {
                     return;
-                }
+                };
 
                 let mut txn = Transaction::new();
                 txn.set_scroll_offsets(
                     external_scroll_id,
                     vec![SampledScrollOffset {
-                        offset,
+                        offset: -offset,
                         generation: 0,
                     }],
                 );

components/compositing/webview_renderer.rs

@@ -8,6 +8,7 @@ use std::collections::{HashMap, VecDeque};
 use std::rc::Rc;
 
 use base::id::{PipelineId, WebViewId};
+use compositing_traits::display_list::ScrollType;
 use compositing_traits::viewport_description::{
     DEFAULT_ZOOM, MAX_ZOOM, MIN_ZOOM, ViewportDescription,
 };
@@ -931,9 +932,11 @@ impl WebViewRenderer {
         {
             let pipeline_details = self.pipelines.get_mut(pipeline_id)?;
             if previous_pipeline_id.replace(pipeline_id) != Some(pipeline_id) {
-                let scroll_result = pipeline_details
-                    .scroll_tree
-                    .scroll_node_or_ancestor(scroll_tree_node, scroll_location);
+                let scroll_result = pipeline_details.scroll_tree.scroll_node_or_ancestor(
+                    scroll_tree_node,
+                    scroll_location,
+                    ScrollType::InputEvents,
+                );
                 if let Some((external_scroll_id, offset)) = scroll_result {
                     return Some(ScrollResult {
                         pipeline_id: *pipeline_id,