Allow positional selectors to match elements without a parent.

third_party/WebKit/Source/core/dom/NthIndexCache.cpp

Index: third_party/WebKit/Source/core/dom/NthIndexCache.cpp
diff --git a/third_party/WebKit/Source/core/dom/NthIndexCache.cpp b/third_party/WebKit/Source/core/dom/NthIndexCache.cpp
index 723f0c477dfe0716f5df084de45ad6efb692c7ad..570c92ca802105c42cc385b5839f8f4d7211a26f 100644
--- a/third_party/WebKit/Source/core/dom/NthIndexCache.cpp
+++ b/third_party/WebKit/Source/core/dom/NthIndexCache.cpp
@@ -81,15 +81,14 @@ unsigned uncachedNthLastOfTypeIndex(Element& element, unsigned& siblingCount) {
 unsigned NthIndexCache::nthChildIndex(Element& element) {
   if (element.isPseudoElement())
     return 1;
-  DCHECK(element.parentNode());
   NthIndexCache* nthIndexCache = element.document().nthIndexCache();
   NthIndexData* nthIndexData = nullptr;
-  if (nthIndexCache && nthIndexCache->m_parentMap)
+  if (element.parentNode() && nthIndexCache && nthIndexCache->m_parentMap)

[rune, 2016/12/20 09:18:47]

If you don't have a parent node, won't N always be one? Then you could do a
parentNode() check with the isPseudoElement() check instead.

     nthIndexData = nthIndexCache->m_parentMap->get(element.parentNode());
   if (nthIndexData)
     return nthIndexData->nthIndex(element);
   unsigned index = uncachedNthChildIndex(element);
-  if (nthIndexCache && index > kCachedSiblingCountLimit)
+  if (element.parentNode() && nthIndexCache && index > kCachedSiblingCountLimit)
     nthIndexCache->cacheNthIndexDataForParent(element);
   return index;
 }
@@ -97,22 +96,20 @@ unsigned NthIndexCache::nthChildIndex(Element& element) {
 unsigned NthIndexCache::nthLastChildIndex(Element& element) {
   if (element.isPseudoElement())
     return 1;
-  DCHECK(element.parentNode());
   NthIndexCache* nthIndexCache = element.document().nthIndexCache();
   NthIndexData* nthIndexData = nullptr;
-  if (nthIndexCache && nthIndexCache->m_parentMap)
+  if (element.parentNode() && nthIndexCache && nthIndexCache->m_parentMap)
     nthIndexData = nthIndexCache->m_parentMap->get(element.parentNode());
   if (nthIndexData)
     return nthIndexData->nthLastIndex(element);
   unsigned index = uncachedNthLastChildIndex(element);
-  if (nthIndexCache && index > kCachedSiblingCountLimit)
+  if (element.parentNode() && nthIndexCache && index > kCachedSiblingCountLimit)
     nthIndexCache->cacheNthIndexDataForParent(element);
   return index;
 }
 
 NthIndexData* NthIndexCache::nthTypeIndexDataForParent(Element& element) const {
-  DCHECK(element.parentNode());
-  if (!m_parentMapForType)
+  if (!m_parentMapForType || !element.parentNode())
     return nullptr;
   if (const IndexByType* map = m_parentMapForType->get(element.parentNode()))
     return map->get(element.tagName());