Don't remove empty display item pairs that draw content

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/RuntimeEnabledFeatures.h"
 #ifndef NDEBUG
@@ skipping 10 matching lines @@
     ASSERT(m_newPaints.isEmpty());
     return m_paintList;
 }
 
 void DisplayItemList::add(WTF::PassOwnPtr<DisplayItem> displayItem)
 {
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
 
     if (displayItem->isEnd()) {
         ASSERT(!m_newPaints.isEmpty());
-        if (m_newPaints.last()->isBegin()) {
+        if (m_newPaints.last()->isBegin() && !m_newPaints.last()->drawsContent()) {
             ASSERT(displayItem->isEndAndPairedWith(*m_newPaints.last()));
             // Remove the beginning display item of this empty pair.
             m_newPaints.removeLast();
 #if ENABLE(ASSERT)
             if (RuntimeEnabledFeatures::slimmingPaintDisplayItemCacheEnabled()) {
                 // Also remove the index pointing to the removed display item.
                 Vector<size_t>& indices = m_newDisplayItemIndicesByClient.find(displayItem->client())->value;
                 if (!indices.isEmpty() && indices.last() == m_newPaints.size())
                     indices.removeLast();
             }
@@ skipping 197 matching lines @@
 #endif // ifndef NDEBUG
 
 void DisplayItemList::replay(GraphicsContext* context)
 {
     updatePaintList();
     for (auto& displayItem : m_paintList)
         displayItem->replay(context);
 }
 
 } // namespace blink