[LayoutNG] Switch NGBreakToken to being RefCounted.

third_party/WebKit/Source/core/layout/ng/ng_block_child_iterator.cc

 // Copyright 2017 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.
 
 #include "core/layout/ng/ng_block_child_iterator.h"
 
 #include "core/layout/ng/ng_block_break_token.h"
 #include "core/layout/ng/ng_layout_input_node.h"
 
 namespace blink {
@@ skipping 16 matching lines @@
     const auto& child_break_tokens = break_token_->ChildBreakTokens();
 
     do {
       // Early exit if we've exhausted our child break tokens.
       if (child_token_idx_ >= child_break_tokens.size())
         break;
 
       // This child break token candidate doesn't match the current node, this
       // node must be unfinished.
       NGBreakToken* child_break_token_candidate =
-          child_break_tokens[child_token_idx_];
+          child_break_tokens[child_token_idx_].get();
       if (child_break_token_candidate->InputNode() != child_)
         break;
 
       ++child_token_idx_;
 
       // We have only found a node if its break token is unfinished.
       if (!child_break_token_candidate->IsFinished()) {
         child_break_token = child_break_token_candidate;
         break;
       }
     } while ((child_ = child_->NextSibling()));
   }
 
   NGLayoutInputNode* child = child_;
   if (child_)
     child_ = child_->NextSibling();
 
   return Entry(child, child_break_token);
 }
 
 }  // namespace blink