compositor: Allow children of layers that don't want scroll events to be

scrolled.

Necessary for `overflow: scroll`.

components/compositing/compositor_layer.rs

@@ -292,13 +292,7 @@ impl CompositorLayer for Layer<CompositorData> {
                            delta: TypedPoint2D<LayerPixel, f32>,
                            cursor: TypedPoint2D<LayerPixel, f32>)
                            -> ScrollEventResult {
-        // If this layer doesn't want scroll events, neither it nor its children can handle scroll
-        // events.
-        if self.wants_scroll_events() != WantsScrollEventsFlag::WantsScrollEvents {
-            return ScrollEventResult::ScrollEventUnhandled;
-        }
-
-        //// Allow children to scroll.
+        // Allow children to scroll.
         let scroll_offset = self.extra_data.borrow().scroll_offset;
         let new_cursor = cursor - scroll_offset;
         for child in self.children().iter() {
@@ -311,6 +305,11 @@ impl CompositorLayer for Layer<CompositorData> {
             }
         }
 
+        // If this layer doesn't want scroll events, it can't handle scroll events.
+        if self.wants_scroll_events() != WantsScrollEventsFlag::WantsScrollEvents {
+            return ScrollEventResult::ScrollEventUnhandled;
+        }
+
         self.clamp_scroll_offset_and_scroll_layer(scroll_offset + delta)
     }