3 files changed, 41 insertions, 37 deletions

diff --git a/components/layout_2020/fragment_tree/fragment.rs b/components/layout_2020/fragment_tree/fragment.rs
index 77b575a9d42..fda4636e9e7 100644
--- a/components/layout_2020/fragment_tree/fragment.rs
+++ b/components/layout_2020/fragment_tree/fragment.rs
@@ -167,6 +167,15 @@ impl Fragment {
         }
     }
 
+    pub fn scrolling_area(&self, containing_block: &PhysicalRect<Length>) -> PhysicalRect<Length> {
+        match self {
+            Fragment::Box(fragment) | Fragment::Float(fragment) => fragment
+                .scrollable_overflow(containing_block)
+                .translate(containing_block.origin.to_vector()),
+            _ => self.scrollable_overflow(containing_block),
+        }
+    }
+
     pub fn scrollable_overflow(
         &self,
         containing_block: &PhysicalRect<Length>,
diff --git a/components/layout_2020/fragment_tree/fragment_tree.rs b/components/layout_2020/fragment_tree/fragment_tree.rs
index 023344a1b6c..f797f5644c6 100644
--- a/components/layout_2020/fragment_tree/fragment_tree.rs
+++ b/components/layout_2020/fragment_tree/fragment_tree.rs
@@ -172,36 +172,26 @@ impl FragmentTree {
         .unwrap_or_else(Rect::zero)
     }
 
-    pub fn get_scroll_area_for_node(&self, requested_node: OpaqueNode) -> Rect<i32> {
-        let mut scroll_area: PhysicalRect<Length> = PhysicalRect::zero();
+    pub fn get_scrolling_area_for_viewport(&self) -> PhysicalRect<Length> {
+        let mut scroll_area = self.initial_containing_block;
+        for fragment in self.root_fragments.iter() {
+            scroll_area = fragment
+                .borrow()
+                .scrolling_area(&self.initial_containing_block)
+                .union(&scroll_area);
+        }
+        scroll_area
+    }
+
+    pub fn get_scrolling_area_for_node(&self, requested_node: OpaqueNode) -> PhysicalRect<Length> {
         let tag_to_find = Tag::new(requested_node);
-        self.find(|fragment, _, containing_block| {
-            if fragment.tag() != Some(tag_to_find) {
-                return None::<()>;
+        let scroll_area = self.find(|fragment, _, containing_block| {
+            if fragment.tag() == Some(tag_to_find) {
+                Some(fragment.scrolling_area(&containing_block))
+            } else {
+                None
             }
-
-            scroll_area = match fragment {
-                Fragment::Box(fragment) | Fragment::Float(fragment) => fragment
-                    .scrollable_overflow(&containing_block)
-                    .translate(containing_block.origin.to_vector()),
-                Fragment::Text(_) |
-                Fragment::AbsoluteOrFixedPositioned(_) |
-                Fragment::Image(_) |
-                Fragment::IFrame(_) |
-                Fragment::Anonymous(_) => return None,
-            };
-            None::<()>
         });
-
-        Rect::new(
-            Point2D::new(
-                scroll_area.origin.x.px() as i32,
-                scroll_area.origin.y.px() as i32,
-            ),
-            Size2D::new(
-                scroll_area.size.width.px() as i32,
-                scroll_area.size.height.px() as i32,
-            ),
-        )
+        scroll_area.unwrap_or_else(PhysicalRect::<Length>::zero)
     }
 }
diff --git a/components/layout_2020/query.rs b/components/layout_2020/query.rs
index e71b5df20ee..3ea4003cd0a 100644
--- a/components/layout_2020/query.rs
+++ b/components/layout_2020/query.rs
@@ -56,7 +56,7 @@ pub struct LayoutThreadData {
     pub scroll_id_response: Option<ExternalScrollId>,
 
     /// A queued response for the scroll {top, left, width, height} of a node in pixels.
-    pub scroll_area_response: Rect<i32>,
+    pub scrolling_area_response: Rect<i32>,
 
     /// A queued response for the resolved style property of an element.
     pub resolved_style_response: String,
@@ -115,9 +115,9 @@ impl LayoutRPC for LayoutRPCImpl {
         }
     }
 
-    fn node_scroll_area(&self) -> NodeGeometryResponse {
+    fn scrolling_area(&self) -> NodeGeometryResponse {
         NodeGeometryResponse {
-            client_rect: self.0.lock().unwrap().scroll_area_response,
+            client_rect: self.0.lock().unwrap().scrolling_area_response,
         }
     }
 
@@ -201,14 +201,19 @@ pub fn process_node_scroll_id_request<'dom>(
 
 /// https://drafts.csswg.org/cssom-view/#scrolling-area
 pub fn process_node_scroll_area_request(
-    requested_node: OpaqueNode,
+    requested_node: Option<OpaqueNode>,
     fragment_tree: Option<Arc<FragmentTree>>,
 ) -> Rect<i32> {
-    if let Some(fragment_tree) = fragment_tree {
-        fragment_tree.get_scroll_area_for_node(requested_node)
-    } else {
-        Rect::zero()
-    }
+    let rect = match (fragment_tree, requested_node) {
+        (Some(tree), Some(node)) => tree.get_scrolling_area_for_node(node),
+        (Some(tree), None) => tree.get_scrolling_area_for_viewport(),
+        _ => return Rect::zero(),
+    };
+
+    Rect::new(
+        Point2D::new(rect.origin.x.px() as i32, rect.origin.y.px() as i32),
+        Size2D::new(rect.size.width.px() as i32, rect.size.height.px() as i32),
+    )
 }
 
 /// Return the resolved value of property for a given (pseudo)element.