[NGFragmentItem] Support list markers

This patch supports adding list markers to |NGFragmentItems|.

List markers are not part of the line box it belongs to in
the |NGPhysicalFragment| tree.

In |NGFragmentItem| world, it is an |NGFragmentItem| in the
inline formatting context in most cases.

When a list marker is attached to a block boxes, there is no
change; i.e., it still appears in the |NGPhysicalFragment|
tree. e.g.,
  <li><div>text</div></li>
then the list marker is propagated to a block formatting
context.

Some tests should turn to pass, but since bots are not setup
yet, I'll update FlagExpectation later.

Bug: 982194
Change-Id: I6af233360d1872de3e9507d69ef3c50275689267
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846627Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706385}

third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.cc

@@ -118,6 +118,13 @@ void NGFragmentItemsBuilder::AddItems(Child* child_begin, Child* child_end) {
   }
 }
 
+void NGFragmentItemsBuilder::AddListMarker(
+    const NGPhysicalBoxFragment& marker_fragment,
+    const LogicalOffset& offset) {
+  items_.push_back(std::make_unique<NGFragmentItem>(marker_fragment, 1));
+  offsets_.push_back(offset);
+}
+
 // Convert internal logical offsets to physical. Items are kept with logical
 // offset until outer box size is determined.
 void NGFragmentItemsBuilder::ConvertToPhysical(WritingMode writing_mode,

third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.h

@@ -49,6 +49,10 @@ class CORE_EXPORT NGFragmentItemsBuilder {
   void AddLine(const NGPhysicalLineBoxFragment& line,
                const LogicalOffset& offset);
 
+  // Add a list marker to the current line.
+  void AddListMarker(const NGPhysicalBoxFragment& marker_fragment,
+                     const LogicalOffset& offset);
+
   // Build a |NGFragmentItems|. The builder cannot build twice because data set
   // to this builder may be cleared.
   void ToFragmentItems(WritingMode writing_mode,

third_party/blink/renderer/core/layout/ng/list/ng_unpositioned_list_marker.cc

@@ -5,6 +5,7 @@
 #include "third_party/blink/renderer/core/layout/ng/list/ng_unpositioned_list_marker.h"
 
 #include "third_party/blink/renderer/core/layout/layout_list_marker.h"
+#include "third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_physical_line_box_fragment.h"
 #include "third_party/blink/renderer/core/layout/ng/list/layout_ng_list_marker.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_box_fragment.h"
@@ -124,6 +125,11 @@ void NGUnpositionedListMarker::AddToBox(
       marker_offset.block_offset);
 
   DCHECK(container_builder);
+  if (NGFragmentItemsBuilder* items_builder =
+          container_builder->ItemsBuilder()) {
+    items_builder->AddListMarker(marker_physical_fragment, marker_offset);
+    return;
+  }
   container_builder->AddChild(marker_physical_fragment, marker_offset);
 }
 
@@ -142,6 +148,7 @@ LayoutUnit NGUnpositionedListMarker::AddToBoxWithoutLineBoxes(
   LogicalOffset offset(InlineOffset(marker_size.inline_size), LayoutUnit());
 
   DCHECK(container_builder);
+  DCHECK(!container_builder->ItemsBuilder());
   container_builder->AddChild(marker_physical_fragment, offset);
 
   return marker_size.block_size;

third_party/blink/renderer/core/layout/ng/ng_box_fragment_builder.cc

@@ -201,6 +201,18 @@ void NGBoxFragmentBuilder::PropagateBreak(
 
 scoped_refptr<const NGLayoutResult> NGBoxFragmentBuilder::ToBoxFragment(
     WritingMode block_or_line_writing_mode) {
+#if DCHECK_IS_ON()
+  if (ItemsBuilder()) {
+    for (const ChildWithOffset& child : Children()) {
+      DCHECK(child.fragment);
+      const NGPhysicalFragment& fragment = *child.fragment;
+      DCHECK(fragment.IsLineBox() ||
+             // TODO(kojii): How to place floats and OOF is TBD.
+             fragment.IsFloatingOrOutOfFlowPositioned());
+    }
+  }
+#endif
+
   if (UNLIKELY(node_ && has_block_fragmentation_)) {
     if (!inline_break_tokens_.IsEmpty()) {
       if (auto token = inline_break_tokens_.back()) {