Show debug information for invalid display items

Source/platform/graphics/paint/DisplayItemList.cpp

 // 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.
 
 #include "config.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 
 #include "platform/NotImplemented.h"
 #include "platform/TraceEvent.h"
 #include "platform/graphics/paint/DrawingDisplayItem.h"
@@ skipping 582 matching lines @@
 #ifndef NDEBUG
 
 WTF::String DisplayItemList::displayItemsAsDebugString(const DisplayItems& list) const
 {
     StringBuilder stringBuilder;
     size_t i = 0;
     for (auto it = list.begin(); it != list.end(); ++it, ++i) {
         const DisplayItem& displayItem = *it;
         if (i)
             stringBuilder.append(",\n");
-        if (!displayItem.isValid()) {
-            stringBuilder.append("null");
-            continue;
-        }
         stringBuilder.append(String::format("{index: %d, ", (int)i));
         displayItem.dumpPropertiesAsDebugString(stringBuilder);
-        stringBuilder.append(", cacheIsValid: ");
-        stringBuilder.append(clientCacheIsValid(displayItem.client()) ? "true" : "false");
+        if (displayItem.isValid()) {
+            stringBuilder.append(", cacheIsValid: ");
+            stringBuilder.append(clientCacheIsValid(displayItem.client()) ? "true" : "false");
+        }
         stringBuilder.append('}');
     }
     return stringBuilder.toString();
 }
 
 void DisplayItemList::showDebugData() const
 {
     WTFLogAlways("current display items: [%s]\n", displayItemsAsDebugString(m_currentDisplayItems).utf8().data());
     WTFLogAlways("new display items: [%s]\n", displayItemsAsDebugString(m_newDisplayItems).utf8().data());
 }
 
 #endif // ifndef NDEBUG
 
 void DisplayItemList::replay(GraphicsContext& context)
 {
     TRACE_EVENT0("blink,benchmark", "DisplayItemList::replay");
     ASSERT(m_newDisplayItems.isEmpty());
     for (DisplayItem& displayItem : m_currentDisplayItems)
         displayItem.replay(context);
 }
 
 } // namespace blink