Auto merge of #14367 - mrobinson:scroll-fragment-point, r=pcwalton

Reimplement scrolling to fragments

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #13736, #10753 (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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This reimplemntation of the feature uses ScrollRootIds to scroll
particular scrollable areas of the page.

Fixes #13736.
Fixes #10753.

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components/layout/flow.rs

@@ -406,7 +406,10 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
     /// Print any extra children (such as fragments) contained in this Flow
     /// for debugging purposes. Any items inserted into the tree will become
     /// children of this flow.
-    fn print_extra_flow_children(&self, _: &mut PrintTree) {
+    fn print_extra_flow_children(&self, _: &mut PrintTree) { }
+
+    fn scroll_root_id(&self) -> ScrollRootId {
+        base(self).scroll_root_id
     }
 }
 

components/layout/query.rs

@@ -12,13 +12,14 @@ use euclid::size::Size2D;
 use flow::{self, Flow};
 use fragment::{Fragment, FragmentBorderBoxIterator, SpecificFragmentInfo};
 use gfx::display_list::{DisplayItemMetadata, DisplayList, OpaqueNode, ScrollOffsetMap};
+use gfx_traits::ScrollRootId;
 use ipc_channel::ipc::IpcSender;
 use opaque_node::OpaqueNodeMethods;
 use script_layout_interface::rpc::{ContentBoxResponse, ContentBoxesResponse};
 use script_layout_interface::rpc::{HitTestResponse, LayoutRPC};
 use script_layout_interface::rpc::{MarginStyleResponse, NodeGeometryResponse};
 use script_layout_interface::rpc::{NodeOverflowResponse, OffsetParentResponse};
-use script_layout_interface::rpc::ResolvedStyleResponse;
+use script_layout_interface::rpc::{NodeScrollRootIdResponse, ResolvedStyleResponse};
 use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutElement, ThreadSafeLayoutNode};
 use script_traits::LayoutMsg as ConstellationMsg;
 use script_traits::UntrustedNodeAddress;
@@ -64,6 +65,9 @@ pub struct LayoutThreadData {
     /// A queued response for the node at a given point
     pub hit_test_response: (Option<DisplayItemMetadata>, bool),
 
+    /// A queued response for the scroll root id for a given node.
+    pub scroll_root_id_response: Option<ScrollRootId>,
+
     /// A pair of overflow property in x and y
     pub overflow_response: NodeOverflowResponse,
 
@@ -178,6 +182,12 @@ impl LayoutRPC for LayoutRPCImpl {
         }
     }
 
+    fn node_scroll_root_id(&self) -> NodeScrollRootIdResponse {
+        NodeScrollRootIdResponse(self.0.lock()
+                                        .unwrap().scroll_root_id_response
+                                        .expect("scroll_root_id is not correctly fetched"))
+    }
+
     /// Retrieves the resolved value for a CSS style property.
     fn resolved_style(&self) -> ResolvedStyleResponse {
         let &LayoutRPCImpl(ref rw_data) = self;
@@ -578,6 +588,11 @@ pub fn process_node_geometry_request<N: LayoutNode>(requested_node: N, layout_ro
     iterator.client_rect
 }
 
+pub fn process_node_scroll_root_id_request<N: LayoutNode>(requested_node: N) -> ScrollRootId {
+    let layout_node = requested_node.to_threadsafe();
+    layout_node.scroll_root_id()
+}
+
 pub fn process_node_scroll_area_request< N: LayoutNode>(requested_node: N, layout_root: &mut Flow)
         -> Rect<i32> {
     let mut iterator = UnioningFragmentScrollAreaIterator::new(requested_node.opaque());