Show debug information for invalid display items

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 0da40fce703c9f7abcd21454f36ee1eb15d5ac22..957556b9352d4b9494a1924332bf64522abed63b 100644
--- a/Source/platform/graphics/paint/DisplayItem.h
+++ b/Source/platform/graphics/paint/DisplayItem.h
@@ -338,14 +338,18 @@ private:
     // constructed at the source location.
     template <typename T, unsigned alignment> friend class ContiguousContainer;
 
-    DisplayItem()
+    DisplayItem(
+#ifndef NDEBUG
+        const String& originalDebugString
+#endif
+        )
         : m_client(nullptr)
         , m_scope(0)
         , m_type(UninitializedType)
         , m_derivedSize(sizeof(*this))
         , m_skippedCache(false)
-#ifndef NDEBUG
-        , m_clientDebugString("invalid")
+#ifdef NDEBUG
+        , m_clientDebugString(originalDebugString)
 #endif
     { }