Utilize NGInlineCursor for inline box traversal

This patch changes "inline_box_traversal.cc" to utilize |NGInlineCursor| instead
of |NGPaintFragment| for preparation of migraing |NGFragmentItem|.

This patch will reduces 1000+ failed web_tests in |LayoutNGFragmentItem| flag.

Bug: 982194
Change-Id: I7f889755ff44beaa63e83f47db415b65969394d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888242
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712949}

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

@@ -650,6 +650,25 @@ void NGInlineCursor::MoveTo(const LayoutObject& layout_object) {
     MoveToNext();
 }
 
+void NGInlineCursor::MoveTo(const NGInlineCursor& cursor) {
+  if (const NGPaintFragment* paint_fragment = cursor.CurrentPaintFragment()) {
+    MoveTo(*paint_fragment);
+    return;
+  }
+  if (cursor.current_item_) {
+    if (!fragment_items_)
+      SetRoot(*cursor.fragment_items_);
+    // Note: We use address instead of iterato because we can't compare
+    // iterators in different span. See |base::CheckedContiguousIterator<T>|.
+    const ptrdiff_t index = &*cursor.item_iter_ - &*items_.begin();
+    DCHECK_GE(index, 0);
+    DCHECK_LT(static_cast<size_t>(index), items_.size());
+    MoveToItem(items_.begin() + index);
+    return;
+  }
+  *this = cursor;
+}
+
 void NGInlineCursor::MoveTo(const NGPaintFragment& paint_fragment) {
   DCHECK(!fragment_items_);
   if (!root_paint_fragment_)

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

@@ -210,6 +210,11 @@ class CORE_EXPORT NGInlineCursor {
   // Functions to move the current position.
   //
 
+  // Move the current position at |cursor|. Unlinke copy constrcutr, this
+  // function doesn't copy root. Note: The current position in |cursor|
+  // should be part of |this| cursor.
+  void MoveTo(const NGInlineCursor& cursor);
+
   // Move the current posint at |paint_fragment|.
   void MoveTo(const NGPaintFragment& paint_fragment);