Improve code readibility of PaintPropertyTreeBuilder

third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h

 // Copyright 2015 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 PaintChunkProperties_h
 #define PaintChunkProperties_h
 
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
@@ skipping 11 matching lines @@
 // properties for a given |PaintChunk|.
 //
 // This differs from |ObjectPaintProperties| because it only stores one property
 // for each type (e.g., either transform or perspective, but not both).
 struct PaintChunkProperties {
     DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 
     PaintChunkProperties() : backfaceHidden(false) { }
 
     // TODO(pdr): Add scroll properties.
-    RefPtr<TransformPaintPropertyNode> transform;
-    RefPtr<ClipPaintPropertyNode> clip;
-    RefPtr<EffectPaintPropertyNode> effect;
+    RefPtr<const TransformPaintPropertyNode> transform;
+    RefPtr<const ClipPaintPropertyNode> clip;
+    RefPtr<const EffectPaintPropertyNode> effect;
     bool backfaceHidden;
 };
 
 // Equality is based only on the pointers and is not 'deep' which would require
 // crawling the entire property tree to compute.
 inline bool operator==(const PaintChunkProperties& a, const PaintChunkProperties& b)
 {
     return a.transform.get() == b.transform.get()
         && a.clip.get() == b.clip.get()
         && a.effect.get() == b.effect.get()
         && a.backfaceHidden == b.backfaceHidden;
 }
 
 inline bool operator!=(const PaintChunkProperties& a, const PaintChunkProperties& b)
 {
     return !(a == b);
 }
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const PaintChunkProperties&, std::ostream*);
 
 } // namespace blink
 
 #endif // PaintChunkProperties_h