Emit dummy display item when recorded picture is empty

Source/platform/graphics/paint/DisplayItem.h

Index: Source/platform/graphics/paint/DisplayItem.h
diff --git a/Source/platform/graphics/paint/DisplayItem.h b/Source/platform/graphics/paint/DisplayItem.h
index b6c5bfcd6d3b0554283b48e6197c6592ebf055ad..30904eeb0600659760646a47916bc6d993b70469 100644
--- a/Source/platform/graphics/paint/DisplayItem.h
+++ b/Source/platform/graphics/paint/DisplayItem.h
@@ -7,6 +7,7 @@
 
 #include "platform/PlatformExport.h"
 #include "wtf/Assertions.h"
+#include "wtf/PassOwnPtr.h"
 
 #ifndef NDEBUG
 #include "wtf/text/StringBuilder.h"
@@ -74,6 +75,8 @@ public:
         Resizer
     };
 
+    static PassOwnPtr<DisplayItem> createDummy(DisplayItemClient, Type);
+
     virtual ~DisplayItem() { }
 
     virtual void replay(GraphicsContext*) = 0;
@@ -91,6 +94,7 @@ public:
     const WTF::String& clientDebugString() const { return m_clientDebugString; }
 
     WTF::String asDebugString() const;
+    virtual const char* name() const = 0;
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const;
 #endif