Make Iris layout dependencies explicit

src/widget/position/scroll_area.rs

@@ -30,7 +30,7 @@ impl Widget for ScrollArea {
         self.tick_fling(now)
     }
 
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         let axis = self.ctl.axis();
         let container_len = painter.px_size().axis(axis);
         self.container_len = container_len;
@@ -41,7 +41,9 @@ impl Widget for ScrollArea {
         self.ctl.set_amt(travelled);
 
         let hint = self.content_len.unwrap_or(container_len);
-        let used = painter.widget_within(&self.inner, self.child_region(hint));
+        let used = painter
+            .widget_within(&self.inner, self.child_region(hint))
+            .size();
 
         let measured = used
             .axis(axis)
@@ -62,7 +64,10 @@ impl Widget for ScrollArea {
             fwd: range - amt,
         });
 
-        painter.place(&self.inner, self.child_region(measured))
+        let size = painter
+            .place(&self.inner, self.child_region(measured))
+            .size();
+        painter.set_size(size);
     }
 }