Make SelectionModifier to use NGInlineCursor

This patch changes |SelectionModifier| to use |NGInlineCursor| instead of
|NGPaintFragment| for prepration of migrating |NGFragmentItem|.

Bug: 982194
Change-Id: I7c962dc3f7e0fd9611b6b83baf5c74d58f4c8e7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1875354
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708923}

third_party/blink/renderer/core/editing/selection_modifier.cc

@@ -159,9 +159,9 @@ base::Optional<TextDirection> DirectionAt(const VisiblePosition& position) {
     return base::nullopt;
 
   if (NGInlineFormattingContextOf(adjusted.GetPosition())) {
-    if (const NGPaintFragment* fragment =
-            ComputeNGCaretPosition(adjusted).PaintFragment())
-      return fragment->PhysicalFragment().ResolvedDirection();
+    const NGInlineCursor& cursor = ComputeNGCaretPosition(adjusted).cursor;
+    if (cursor)
+      return cursor.CurrentResolvedDirection();
     return base::nullopt;
   }
 
@@ -181,11 +181,11 @@ base::Optional<TextDirection> LineDirectionAt(const VisiblePosition& position) {
     return base::nullopt;
 
   if (NGInlineFormattingContextOf(adjusted.GetPosition())) {
-    if (const NGPaintFragment* fragment =
-            ComputeNGCaretPosition(adjusted).PaintFragment()) {
-      return ParagraphDirectionOf(*fragment);
-    }
-    return base::nullopt;
+    NGInlineCursor line = ComputeNGCaretPosition(adjusted).cursor;
+    if (!line)
+      return base::nullopt;
+    line.MoveToContainingLine();
+    return line.CurrentBaseDirection();
   }
 
   if (const InlineBox* box =