Emit dummy display item when recorded picture is empty

Source/platform/graphics/paint/TransparencyDisplayItem.h

Index: Source/platform/graphics/paint/TransparencyDisplayItem.h
diff --git a/Source/platform/graphics/paint/TransparencyDisplayItem.h b/Source/platform/graphics/paint/TransparencyDisplayItem.h
index 33f60b45837212477699602de3b60e535566460a..f3929dad7b10c2f49bbc4bb6d212ed122441a463 100644
--- a/Source/platform/graphics/paint/TransparencyDisplayItem.h
+++ b/Source/platform/graphics/paint/TransparencyDisplayItem.h
@@ -25,6 +25,7 @@ public:
 
 private:
 #ifndef NDEBUG
+    virtual const char* name() const override { return "BeginTransparency"; }
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const override;
 #endif
 
@@ -53,6 +54,11 @@ public:
 protected:
     EndTransparencyDisplayItem(DisplayItemClient client, Type type)
         : DisplayItem(client, type) { }
+
+private:
+#ifndef NDEBUG
+    virtual const char* name() const override { return "EndTransparency"; }
+#endif
 };
 
 } // namespace blink