Show debug information for invalid display items

Source/platform/graphics/paint/DisplayItem.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 DisplayItem_h
 #define DisplayItem_h
 
 #include "platform/PlatformExport.h"
 #include "platform/graphics/ContiguousContainer.h"
 #include "platform/graphics/paint/DisplayItemClient.h"
@@ skipping 320 matching lines @@
     WTF::String asDebugString() const;
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const;
 #endif
 
 private:
     // The default DisplayItem constructor is only used by
     // ContiguousContainer::appendByMoving where an invalid DisplaItem is
     // 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
     { }
 
     DisplayItemClient m_client;
     unsigned m_scope;
     static_assert(TypeLast < (1 << 16), "DisplayItem::Type should fit in 16 bits");
     const Type m_type : 16;
     unsigned m_derivedSize : 8; // size of the actual derived class
     unsigned m_skippedCache : 1;
 
@@ skipping 18 matching lines @@
     bool isEndAndPairedWith(DisplayItem::Type otherType) const override = 0;
 #endif
 
 private:
     bool isEnd() const final { return true; }
 };
 
 } // namespace blink
 
 #endif // DisplayItem_h