Use a StringImpl* instead of an AtomicString for NodeListAtomicNameCacheMap's key

Source/core/dom/NodeRareData.h

Index: Source/core/dom/NodeRareData.h
diff --git a/Source/core/dom/NodeRareData.h b/Source/core/dom/NodeRareData.h
index 403a0b2cc7492bba5265d8653d530301231c13e1..950f3946dbfc98f5f429ae0ee1c0353671eff493 100644
--- a/Source/core/dom/NodeRareData.h
+++ b/Source/core/dom/NodeRareData.h
@@ -94,7 +94,16 @@ public:
         static const bool safeToCompareToEmptyOrDeleted = DefaultHash<StringType>::Hash::safeToCompareToEmptyOrDeleted;
     };
 
-    typedef HashMap<std::pair<unsigned char, AtomicString>, LiveNodeListBase*, NodeListCacheMapEntryHash<AtomicString> > NodeListAtomicNameCacheMap;
+    struct NodeListAtomicCacheMapEntryHash {
+        static unsigned hash(const std::pair<unsigned char, StringImpl*>& entry)
+        {
+            return DefaultHash<StringImpl*>::Hash::hash(entry.second) + entry.first;
+        }
+        static bool equal(const std::pair<unsigned char, StringImpl*>& a, const std::pair<unsigned char, StringImpl*>& b) { return a == b; }
+        static const bool safeToCompareToEmptyOrDeleted = DefaultHash<StringImpl*>::Hash::safeToCompareToEmptyOrDeleted;
+    };
+
+    typedef HashMap<std::pair<unsigned char, StringImpl*>, LiveNodeListBase*, NodeListAtomicCacheMapEntryHash> NodeListAtomicNameCacheMap;
     typedef HashMap<std::pair<unsigned char, String>, LiveNodeListBase*, NodeListCacheMapEntryHash<String> > NodeListNameCacheMap;
     typedef HashMap<QualifiedName, TagCollection*> TagCollectionCacheNS;
 
@@ -228,9 +237,9 @@ private:
         : m_childNodeList(0)
     { }
 
-    std::pair<unsigned char, AtomicString> namedNodeListKey(CollectionType type, const AtomicString& name)
+    std::pair<unsigned char, StringImpl*> namedNodeListKey(CollectionType type, const AtomicString& name)
     {
-        return std::pair<unsigned char, AtomicString>(type, name);
+        return std::pair<unsigned char, StringImpl*>(type, name.impl());

[abarth-chromium, 2014/02/09 03:46:27]

Why is this memory safe?  What retains |name| ?

[Inactive, 2014/02/09 14:06:54]

Nothing retains name. This is safe because we are never doing anything with this
StringImpl* besides pointer comparison. It merely serves as a unique identifier
in the HashTable. It seems to be quite common in Blink to use atomic StringImpl*
for keys in Hash Tables without ref'ing them (see for e.g.
DocumentOrderedMap.h).

[Inactive, 2014/02/09 14:28:02]

Never mind my previous comment, it is inaccurate. The AtomicStrings are retained
by the NodeLists (e.g. HTMLNameCollection.m_name, TagCollection.m_localName,
...). And the node lists are in charge of removing themselves from the cache on
deletion. 

     }
 
     std::pair<unsigned char, String> namedNodeListKey(CollectionType type, const String& name)