fix!: Drop Tree::root_scroller (#279)

bindings/c/src/common.rs

@@ -873,24 +873,19 @@ impl node_builder {
 #[repr(C)]
 pub struct tree {
     pub root: node_id,
-    pub root_scroller: opt_node_id,
 }
 
 impl tree {
     #[no_mangle]
     pub extern "C" fn accesskit_tree_new(root: node_id) -> tree {
-        tree {
-            root,
-            root_scroller: opt_node_id::default(),
-        }
+        tree { root }
     }
 }
 
 impl From<tree> for Tree {
     fn from(tree: tree) -> Self {
         Self {
             root: tree.root.into(),
-            root_scroller: tree.root_scroller.into(),
         }
     }
 }

common/src/lib.rs

@@ -2336,20 +2336,12 @@ impl JsonSchema for Node {
 #[cfg_attr(feature = "serde", serde(rename_all = "camelCase"))]
 pub struct Tree {
     pub root: NodeId,
-
-    /// The node that's used as the root scroller, if any. On some platforms
-    /// like Android we need to ignore accessibility scroll offsets for
-    /// that node and get them from the viewport instead.
-    pub root_scroller: Option<NodeId>,
 }
 
 impl Tree {
     #[inline]
     pub fn new(root: NodeId) -> Tree {
-        Tree {
-            root,
-            root_scroller: None,
-        }
+        Tree { root }
     }
 }
 

consumer/src/tree.rs

@@ -33,9 +33,6 @@ impl State {
     fn validate_global(&self) {
         assert!(self.nodes.contains_key(&self.data.root));
         assert!(self.nodes.contains_key(&self.focus));
-        if let Some(id) = self.data.root_scroller {
-            assert!(self.nodes.contains_key(&id));
-        }
     }
 
     fn update(