Auto merge of #9968 - izgzhen:scroll, r=asajeffrey

Implement scroll, scrollLeft, scrollTop and friends, addressing issue #9650

This is a work in progress to solve https://github.com/servo/servo/issues/9650. Thanks a lot for helping the review.

- [x] scroll
- [x] scrollTo
- [x] scrollBy
- [x] scrollTop (setter and getter)
- [x] scrollLeft (setter and getter)

The setters will be implemented in another PR after this is merged.

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components/script/layout_interface.rs

@@ -23,7 +23,7 @@ use std::sync::Arc;
 use std::sync::mpsc::{Receiver, Sender, channel};
 use string_cache::Atom;
 use style::context::ReflowGoal;
-use style::properties::longhands::{margin_top, margin_right, margin_bottom, margin_left};
+use style::properties::longhands::{margin_top, margin_right, margin_bottom, margin_left, overflow_x};
 use style::selector_impl::PseudoElement;
 use style::servo::Stylesheet;
 use url::Url;
@@ -104,8 +104,12 @@ 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 overflow-x and overflow-y of this node. Used by `scrollTop` etc.
+    fn node_overflow(&self) -> NodeOverflowResponse;
     /// Requests the scroll geometry of this node. Used by APIs such as `scrollTop`.
     fn node_scroll_area(&self) -> NodeGeometryResponse;
+    /// Requests the layer id of this node. Used by APIs such as `scrollTop`
+    fn node_layer_id(&self) -> NodeLayerIdResponse;
     /// Requests the node containing the point of interest
     fn hit_test(&self) -> HitTestResponse;
     /// Query layout for the resolved value of a given CSS property
@@ -136,6 +140,8 @@ impl MarginStyleResponse {
     }
 }
 
+pub struct NodeOverflowResponse(pub Option<Point2D<overflow_x::computed_value::T>>);
+
 pub struct ContentBoxResponse(pub Rect<Au>);
 pub struct ContentBoxesResponse(pub Vec<Rect<Au>>);
 pub struct HitTestResponse {
@@ -144,6 +150,11 @@ pub struct HitTestResponse {
 pub struct NodeGeometryResponse {
     pub client_rect: Rect<i32>,
 }
+
+pub struct NodeLayerIdResponse {
+    pub layer_id: LayerId,
+}
+
 pub struct ResolvedStyleResponse(pub Option<String>);
 
 #[derive(Clone)]
@@ -167,8 +178,10 @@ pub enum ReflowQueryType {
     NoQuery,
     ContentBoxQuery(TrustedNodeAddress),
     ContentBoxesQuery(TrustedNodeAddress),
+    NodeOverflowQuery(TrustedNodeAddress),
     HitTestQuery(Point2D<f32>, bool),
     NodeGeometryQuery(TrustedNodeAddress),
+    NodeLayerIdQuery(TrustedNodeAddress),
     NodeScrollGeometryQuery(TrustedNodeAddress),
     ResolvedStyleQuery(TrustedNodeAddress, Option<PseudoElement>, Atom),
     OffsetParentQuery(TrustedNodeAddress),