Emit dummy display item when recorded picture is empty

Source/platform/graphics/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 "platform/geometry/LayoutRect.h"
 #include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "public/platform/WebBlendMode.h"
 #include "wtf/PassOwnPtr.h"
 #ifndef NDEBUG
 #include "wtf/text/WTFString.h"
 #endif
 
 namespace blink {
 
 class PLATFORM_EXPORT BeginTransparencyDisplayItem : public DisplayItem {
 public:
     static PassOwnPtr<BeginTransparencyDisplayItem> create(DisplayItemClient client, Type type, const CompositeOperator compositeOperator, const WebBlendMode& blendMode, const float opacity) { return adoptPtr(new BeginTransparencyDisplayItem(client, type, compositeOperator, blendMode, opacity)); }
 
     virtual void replay(GraphicsContext*) override;
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override;
 
 private:
 #ifndef NDEBUG
+    virtual const char* name() const override { return "BeginTransparency"; }
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const override;
 #endif
 
     bool hasBlendMode() const { return m_blendMode != WebBlendModeNormal; }
 
 protected:
     BeginTransparencyDisplayItem(DisplayItemClient client, Type type, const CompositeOperator compositeOperator, const WebBlendMode& blendMode, const float opacity)
         : DisplayItem(client, type)
         , m_compositeOperator(compositeOperator)
         , m_blendMode(blendMode)
         , m_opacity(opacity) { }
 
 private:
     const CompositeOperator m_compositeOperator;
     const WebBlendMode m_blendMode;
     const float m_opacity;
 };
 
 class PLATFORM_EXPORT EndTransparencyDisplayItem : public DisplayItem {
 public:
     static PassOwnPtr<EndTransparencyDisplayItem> create(DisplayItemClient client, Type type) { return adoptPtr(new EndTransparencyDisplayItem(client, type)); }
 
     virtual void replay(GraphicsContext*) override;
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override;
 
 protected:
     EndTransparencyDisplayItem(DisplayItemClient client, Type type)
         : DisplayItem(client, type) { }
+
+private:
+#ifndef NDEBUG
+    virtual const char* name() const override { return "EndTransparency"; }
+#endif
 };
 
 } // namespace blink
 
 #endif // TransparencyDisplayItem_h