servo: Merge #9824 - Add the scrollWidth and scrollHeight extensions to the element interface (from danlrobertson:element1); r=asajeffrey

Add the `scrollWidth` and `scrollHeight` extensions to the element interface. My goal was to create a method that encompassed getting `scrollWidth`, `scrollHeight`, `scrollTop`, and `scrollLeft`.

I also noted that `clientHeight` and `clientWidth` to not handle the root element and the body element correctly.

Source-Repo: https://github.com/servo/servo
Source-Revision: 7ff7932a8cb15c42a436958e953cc904ba7a0bd8

servo/components/script/layout_interface.rs

@@ -104,6 +104,8 @@ pub trait LayoutRPC {
     fn content_boxes(&self) -> ContentBoxesResponse;
     /// Requests the geometry of this node. Used by APIs such as `clientTop`.
     fn node_geometry(&self) -> NodeGeometryResponse;
+    /// Requests the scroll geometry of this node. Used by APIs such as `scrollTop`.
+    fn node_scroll_area(&self) -> NodeGeometryResponse;
     /// Requests the node containing the point of interest
     fn hit_test(&self) -> HitTestResponse;
     /// Query layout for the resolved value of a given CSS property
@@ -165,6 +167,7 @@ pub enum ReflowQueryType {
     ContentBoxesQuery(TrustedNodeAddress),
     HitTestQuery(Point2D<f32>, bool),
     NodeGeometryQuery(TrustedNodeAddress),
+    NodeScrollGeometryQuery(TrustedNodeAddress),
     ResolvedStyleQuery(TrustedNodeAddress, Option<PseudoElement>, Atom),
     OffsetParentQuery(TrustedNodeAddress),
     MarginStyleQuery(TrustedNodeAddress),