[LayoutNG] Switch NGConstraintSpace to being RefCounted.

third_party/WebKit/Source/core/layout/ng/ng_line_builder.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 NGLineBuilder_h
 #define NGLineBuilder_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_physical_fragment.h"
 #include "core/layout/ng/ng_units.h"
@@ skipping 122 matching lines @@
     // Include |InlineItemMetrics| into the metrics for this line box.
     void UpdateMaxAscentAndDescent(const InlineItemMetrics&);
   };
 
   void PlaceItems(const Vector<LineItemChunk, 32>&);
   void AccumulateUsedFonts(const NGLayoutInlineItem&,
                            const LineItemChunk&,
                            LineBoxData*);
 
   Persistent<NGInlineNode> inline_box_;
-  Persistent<const NGConstraintSpace> constraint_space_;
+  const NGConstraintSpace* constraint_space_;  // Not owned as STACK_ALLOCATED.
   Vector<RefPtr<NGPhysicalFragment>, 32> fragments_;
   Vector<NGLogicalOffset, 32> offsets_;
   Vector<LineBoxData, 32> line_box_data_list_;
   unsigned start_index_ = 0;
   unsigned start_offset_ = 0;
   unsigned last_index_ = 0;
   unsigned end_offset_ = 0;
   unsigned last_break_opportunity_index_ = 0;
   unsigned last_break_opportunity_offset_ = 0;
   LayoutUnit end_position_;
   LayoutUnit last_break_opportunity_position_;
   LayoutUnit content_size_;
   LayoutUnit max_inline_size_;
   FontBaseline baseline_type_;
 
 #if DCHECK_IS_ON()
   unsigned is_bidi_reordered_ : 1;
 #endif
 };
 
 }  // namespace blink
 
 #endif  // NGLineBuilder_h