Avoid empty display item pairs

Source/platform/graphics/paint/DisplayItemList.cpp

Index: Source/platform/graphics/paint/DisplayItemList.cpp
diff --git a/Source/platform/graphics/paint/DisplayItemList.cpp b/Source/platform/graphics/paint/DisplayItemList.cpp
index 654b7f0f91cdd8b22e890f7a4ffc863255fe0217..783e1589c55b89f870bc610c822d9b4de3811b56 100644
--- a/Source/platform/graphics/paint/DisplayItemList.cpp
+++ b/Source/platform/graphics/paint/DisplayItemList.cpp
@@ -25,6 +25,16 @@ const PaintList& DisplayItemList::paintList()
 void DisplayItemList::add(WTF::PassOwnPtr<DisplayItem> displayItem)
 {
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
+
+    if (displayItem->isEnd()) {
+        ASSERT(!m_newPaints.isEmpty());
+        if (m_newPaints.last()->isBegin()) {
+            ASSERT(displayItem->isEndAndPairedWith(*m_newPaints.last()));
+            // Remove empty pairs.
+            m_newPaints.removeLast();
+            return;
+        }
+    }
     m_newPaints.append(displayItem);
 }