Add static root property tree nodes [spv2]

third_party/WebKit/Source/platform/graphics/paint/ClipPaintPropertyNode.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 ClipPaintPropertyNode_h
 #define ClipPaintPropertyNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatRoundedRect.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
@@ skipping 24 matching lines @@
         m_parent = parent;
         m_localTransformSpace = localTransformSpace;
         m_clipRect = clipRect;
     }
 
     const TransformPaintPropertyNode* localTransformSpace() const { return m_localTransformSpace.get(); }
     const FloatRoundedRect& clipRect() const { return m_clipRect; }
 
     // Reference to inherited clips, or nullptr if this is the only clip.
     const ClipPaintPropertyNode* parent() const { return m_parent.get(); }
+    bool isRoot() const { return !m_parent; }

[chrishtr, 2016/09/22 16:36:57]

You never use this method outside of tests. why add it?

[pdr., 2016/09/22 19:48:21]

It's also used in the property tree printer. I think we'll start using it for
real in the followup when root layer scrolls begins using the root nodes. For
example, we can dcheck that the root nodes aren't modified. We could do a
private/friend approach but I don't think we will want to hide the root node
concept.

 
 private:
     ClipPaintPropertyNode(PassRefPtr<const ClipPaintPropertyNode> parent, PassRefPtr<const TransformPaintPropertyNode> localTransformSpace, const FloatRoundedRect& clipRect)
         : m_parent(parent), m_localTransformSpace(localTransformSpace), m_clipRect(clipRect) { }
 
     RefPtr<const ClipPaintPropertyNode> m_parent;
     RefPtr<const TransformPaintPropertyNode> m_localTransformSpace;
     FloatRoundedRect m_clipRect;
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const ClipPaintPropertyNode&, std::ostream*);
 
 } // namespace blink
 
 #endif // ClipPaintPropertyNode_h