[LayoutNG] Switch NGBreakToken to being RefCounted.

third_party/WebKit/Source/core/layout/ng/ng_text_layout_algorithm.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NGInlineLayoutAlgorithm_h
 #define NGInlineLayoutAlgorithm_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_break_token.h"
 #include "core/layout/ng/ng_layout_algorithm.h"
@@ skipping 20 matching lines @@
   NGTextLayoutAlgorithm(NGInlineNode* inline_box,
                         NGConstraintSpace* space,
                         NGBreakToken* break_token = nullptr);
 
   RefPtr<NGLayoutResult> Layout() override;
   void LayoutInline(NGLineBuilder*);
 
  private:
   Persistent<NGInlineNode> inline_box_;
   NGConstraintSpace* constraint_space_;
-  Persistent<NGBreakToken> break_token_;
+  NGBreakToken* break_token_;
 
   friend class NGInlineNodeTest;
 };
 
 }  // namespace blink
 
 #endif  // NGInlineLayoutAlgorithm_h