[LayoutNG] Make NGBlockNode return a const style reference.

third_party/WebKit/Source/core/layout/ng/ng_block_node.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 NGBlockNode_h
 #define NGBlockNode_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_layout_input_node.h"
 #include "core/layout/ng/ng_physical_box_fragment.h"
@@ skipping 25 matching lines @@
   NGPhysicalFragment* Layout(NGConstraintSpace* constraint_space) override;
   NGBlockNode* NextSibling() override;
   LayoutObject* GetLayoutObject() override;
 
   // Computes the value of min-content and max-content for this box.
   // If the underlying layout algorithm returns NotImplemented from
   // ComputeMinAndMaxContentSizes, this function will synthesize these sizes
   // using Layout with special constraint spaces.
   MinAndMaxContentSizes ComputeMinAndMaxContentSizes();
 
-  const ComputedStyle* Style() const;
-  ComputedStyle* MutableStyle();
+  const ComputedStyle& Style() const;
 
   NGLayoutInputNode* FirstChild();
 
   void SetNextSibling(NGBlockNode*);
   void SetFirstChild(NGLayoutInputNode*);
 
   void SetFragment(NGPhysicalBoxFragment* fragment) { fragment_ = fragment; }
   NGBreakToken* CurrentBreakToken() const;
   bool IsLayoutFinished() const {
     return fragment_ && !fragment_->BreakToken();
@@ skipping 34 matching lines @@
 
 DEFINE_TYPE_CASTS(NGBlockNode,
                   NGLayoutInputNode,
                   node,
                   node->Type() == NGLayoutInputNode::kLegacyBlock,
                   node.Type() == NGLayoutInputNode::kLegacyBlock);
 
 }  // namespace blink
 
 #endif  // NGBlockNode