Auto merge of #17690 - stshine:no-inorder, r=emilio

layout: Stop in-order traversal on children of InlineFlow

No need to do in-order traversal for children of InlineFlow, since
they are either inline-block or absolutely positioned elements, which
are guaranteed to be block formatting context.

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components/layout/inline.rs

@@ -1420,6 +1420,8 @@ impl Flow for InlineFlow {
     }
 
     /// Calculate and set the block-size of this flow. See CSS 2.1 § 10.6.1.
+    /// Note that we do not need to do in-order traversal becase the children
+    /// are always block formatting context.
     fn assign_block_size(&mut self, layout_context: &LayoutContext) {
         let _scope = layout_debug_scope!("inline::assign_block_size {:x}",
                                          self.base.debug_id());
@@ -1484,19 +1486,6 @@ impl Flow for InlineFlow {
             indentation = Au(0)
         }
 
-        // Assign block sizes for any inline-block descendants.
-        let thread_id = self.base.thread_id;
-        for kid in self.base.child_iter_mut() {
-            if flow::base(kid).flags.contains(IS_ABSOLUTELY_POSITIONED) ||
-                    flow::base(kid).flags.is_float() {
-                continue
-            }
-            let content_box = flow::base(kid).position;
-            kid.assign_block_size_for_inorder_child_if_necessary(layout_context,
-                                                                 thread_id,
-                                                                 content_box);
-        }
-
         if self.contains_positioned_fragments() {
             // Assign block-sizes for all flows in this absolute flow tree.
             // This is preorder because the block-size of an absolute flow may depend on