Improve code readibility of PaintPropertyTreeBuilder

third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.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 PropertyTreeState_h
 #define PropertyTreeState_h
 
 #include "wtf/HashFunctions.h"
 #include "wtf/HashTraits.h"
 
 namespace blink {
 
 class TransformPaintPropertyNode;
 class ClipPaintPropertyNode;
 class EffectPaintPropertyNode;
 
 // Represents the combination of transform, clip and effect nodes for a particular coordinate space.
 // See GeometryMapper.
 struct PropertyTreeState {
     PropertyTreeState() : PropertyTreeState(nullptr, nullptr, nullptr) {}
 
     PropertyTreeState(
-        TransformPaintPropertyNode* transform,
-        ClipPaintPropertyNode* clip,
-        EffectPaintPropertyNode* effect)
+        const TransformPaintPropertyNode* transform,
+        const ClipPaintPropertyNode* clip,
+        const EffectPaintPropertyNode* effect)
     : transform(transform), clip(clip), effect(effect) {}
 
-    RefPtr<TransformPaintPropertyNode> transform;
-    RefPtr<ClipPaintPropertyNode> clip;
-    RefPtr<EffectPaintPropertyNode> effect;
+    RefPtr<const TransformPaintPropertyNode> transform;
+    RefPtr<const ClipPaintPropertyNode> clip;
+    RefPtr<const EffectPaintPropertyNode> effect;
 };
 
 template <class A>
 unsigned propertyTreeNodeDepth(const A* node)
 {
     unsigned depth = 0;
     while (node) {
         depth++;
         node = node->parent();
     }
@@ skipping 23 matching lines @@
     while (a != b) {
         a = a->parent();
         b = b->parent();
     }
     return a;
 }
 
 } // namespace blink
 
 #endif // PropertyTreeState_h