DisplayItemPropertyTreeBuilder: Support (2D) transform and scroll display items.

Source/platform/graphics/paint/TransformDisplayItem.h

 // Copyright 2014 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 TransformDisplayItem_h
 #define TransformDisplayItem_h
 
 #include "platform/graphics/paint/DisplayItem.h"
 #include "platform/transforms/AffineTransform.h"
 #include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
 class PLATFORM_EXPORT BeginTransformDisplayItem final : public PairedBeginDisplayItem {
 public:
     BeginTransformDisplayItem(const DisplayItemClientWrapper& client, const AffineTransform& transform)
         : PairedBeginDisplayItem(client, BeginTransform, sizeof(*this))
         , m_transform(transform) { }
 
     void replay(GraphicsContext&) override;
     void appendToWebDisplayItemList(WebDisplayItemList*) const override;
 
+    const AffineTransform& transform() const { return m_transform; }
+
 private:
 #ifndef NDEBUG
     void dumpPropertiesAsDebugString(WTF::StringBuilder&) const final;
 #endif
 
+private:
     const AffineTransform m_transform;
 };
 
 class PLATFORM_EXPORT EndTransformDisplayItem final : public PairedEndDisplayItem {
 public:
     EndTransformDisplayItem(const DisplayItemClientWrapper& client)
         : PairedEndDisplayItem(client, EndTransform, sizeof(*this)) { }
 
     void replay(GraphicsContext&) override;
     void appendToWebDisplayItemList(WebDisplayItemList*) const override;
 
 private:
 #if ENABLE(ASSERT)
     bool isEndAndPairedWith(DisplayItem::Type otherType) const final { return otherType == BeginTransform; }
 #endif
 };
 
 } // namespace blink
 
 #endif // TransformDisplayItem_h