Add `explicit` to NGInlineBackwardCursor constructor

Bug: 982194
Change-Id: I763b6c4d632350db15bb4f32351c8a48ff1776ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2164350
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762555}
diff --git a/third_party/blink/renderer/core/layout/ng/inline/ng_inline_cursor.h b/third_party/blink/renderer/core/layout/ng/inline/ng_inline_cursor.h
index fa129796..df846cc2 100644
--- a/third_party/blink/renderer/core/layout/ng/inline/ng_inline_cursor.h
+++ b/third_party/blink/renderer/core/layout/ng/inline/ng_inline_cursor.h
@@ -182,8 +182,8 @@
   explicit NGInlineCursor(const NGFragmentItems& fragment_items,
                           ItemsSpan items);
   explicit NGInlineCursor(const NGPaintFragment& root_paint_fragment);
+  explicit NGInlineCursor(const NGInlineBackwardCursor& backward_cursor);
   NGInlineCursor(const NGInlineCursor& other) = default;
-  NGInlineCursor(const NGInlineBackwardCursor& backward_cursor);
 
   // Creates an |NGInlineCursor| without the root. Even when callers don't know
   // the root of the inline formatting context, this cursor can |MoveTo()|
@@ -463,7 +463,7 @@
  public:
   // |cursor| should be the first child of root or descendants, e.g. the first
   // item in |NGInlineCursor::items_|.
-  NGInlineBackwardCursor(const NGInlineCursor& cursor);
+  explicit NGInlineBackwardCursor(const NGInlineCursor& cursor);
 
   const NGInlineCursorPosition& Current() const { return current_; }
   operator bool() const { return Current(); }