[FragmentItem] Use |NGInlineCursorPosition| in |MoveToLastForSameLayoutObject|

|MoveToLastForSameLayoutObject| saves |NGInlineCursor|
because it was written before |NGInlineCursorPosition| was
added. This patch changes to save |NGInlineCursorPosition|,
saving a bit of memory bandwidth.

This patch has no behavior changes.

Bug: 982194
Change-Id: Ia1b8ddbf303c2823b2f72e8f24883435602d8399
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2120372Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753503}

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

@@ -1076,12 +1076,14 @@ void NGInlineCursor::MoveToLastChild() {
 }
 
 void NGInlineCursor::MoveToLastForSameLayoutObject() {
-  NGInlineCursor last;
-  while (IsNotNull()) {
-    last = *this;
+  if (!Current())
+    return;
+  NGInlineCursorPosition last;
+  do {
+    last = Current();
     MoveToNextForSameLayoutObject();
-  }
-  *this = last;
+  } while (Current());
+  MoveTo(last);
 }
 
 void NGInlineCursor::MoveToLastLogicalLeaf() {