Enable fast/images with slimming paint

Source/core/paint/TransparencyDisplayItem.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 TransparencyDisplayItem_h
 #define TransparencyDisplayItem_h
 
 #include "core/paint/ViewDisplayList.h"
 #include "platform/geometry/LayoutRect.h"
 #include "public/platform/WebBlendMode.h"
 
 namespace blink {
 
+// FIXME: Move this file to TransparencyRecorder
+
 class BeginTransparencyDisplayItem : public DisplayItem {
 public:
     BeginTransparencyDisplayItem(const RenderObject* renderer, Type type, const LayoutRect& clipRect, const WebBlendMode& blendMode, const float opacity)
         : DisplayItem(renderer, type)
         , m_clipRect(clipRect)
         , m_blendMode(blendMode)
         , m_opacity(opacity) { }
     virtual void replay(GraphicsContext*) override;
 
 private:
@@ skipping 13 matching lines @@
     EndTransparencyDisplayItem(const RenderObject* renderer, Type type)
         : DisplayItem(renderer, type) { }
     virtual void replay(GraphicsContext*) override;
 
 private:
 #ifndef NDEBUG
     virtual WTF::String asDebugString() const override;
 #endif
 };
 
+class TransparencyRecorder {
+public:
+    explicit TransparencyRecorder(GraphicsContext*, const RenderObject*, DisplayItem::Type, const LayoutRect& clipRect, const WebBlendMode&, const float opacity);
+
+    ~TransparencyRecorder();
+
+private:
+    const RenderObject* m_renderer;
+    const DisplayItem::Type m_type;
+    GraphicsContext* m_graphicsContext;
+};
+
 } // namespace blink
 
 #endif // TransparencyDisplayItem_h