[LayoutNG] Switch NGConstraintSpace to being RefCounted.

third_party/WebKit/Source/core/layout/ng/ng_constraint_space_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 NGConstraintSpaceBuilder_h
 #define NGConstraintSpaceBuilder_h
 
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_units.h"
 #include "wtf/Allocator.h"
@@ skipping 45 matching lines @@
       const WTF::Optional<LayoutUnit>& clearance_offset);
 
   // Creates a new constraint space. This may be called multiple times, for
   // example the constraint space will be different for a child which:
   //  - Establishes a new formatting context.
   //  - Is within a fragmentation container and needs its fragmentation offset
   //    updated.
   //  - Has its size is determined by its parent layout (flex, abs-pos).
   //
   // NGWritingMode specifies the writing mode of the generated space.
-  NGConstraintSpace* ToConstraintSpace(NGWritingMode);
+  RefPtr<NGConstraintSpace> ToConstraintSpace(NGWritingMode);
 
  private:
   // Relative to parent_writing_mode_.
   NGLogicalSize available_size_;
   // Relative to parent_writing_mode_.
   NGLogicalSize percentage_resolution_size_;
   NGPhysicalSize initial_containing_block_size_;
   LayoutUnit fragmentainer_space_available_;
 
   unsigned parent_writing_mode_ : 2;
   unsigned is_fixed_size_inline_ : 1;
   unsigned is_fixed_size_block_ : 1;
   unsigned is_shrink_to_fit_ : 1;
   unsigned is_inline_direction_triggers_scrollbar_ : 1;
   unsigned is_block_direction_triggers_scrollbar_ : 1;
   unsigned fragmentation_type_ : 2;
   unsigned is_new_fc_ : 1;
   unsigned is_anonymous_ : 1;
   unsigned text_direction_ : 1;
 
   NGMarginStrut margin_strut_;
   NGLogicalOffset bfc_offset_;
   std::shared_ptr<NGExclusions> exclusions_;
   WTF::Optional<LayoutUnit> clearance_offset_;
 };
 
 }  // namespace blink
 
 #endif  // NGConstraintSpaceBuilder