Support tag names as invalidation set features.

Source/core/css/invalidation/DescendantInvalidationSet.cpp

Index: Source/core/css/invalidation/DescendantInvalidationSet.cpp
diff --git a/Source/core/css/invalidation/DescendantInvalidationSet.cpp b/Source/core/css/invalidation/DescendantInvalidationSet.cpp
index e378c194610e672f73ab43df5257ca7b26a5cb02..a1b55be1008e9711ce06d7e9bd0c84b67bcc0c84 100644
--- a/Source/core/css/invalidation/DescendantInvalidationSet.cpp
+++ b/Source/core/css/invalidation/DescendantInvalidationSet.cpp
@@ -161,6 +161,14 @@ void DescendantInvalidationSet::getIds(Vector<AtomicString>& ids) const
         ids.append(*it);
 }
 
+void DescendantInvalidationSet::getTagNames(Vector<AtomicString>& tagNames) const
+{
+    if (!m_tagNames)
+        return;
+    for (HashSet<AtomicString>::const_iterator it = m_tagNames->begin(); it != m_tagNames->end(); ++it)
+        tagNames.append(*it);
+}
+
 void DescendantInvalidationSet::setWholeSubtreeInvalid()
 {
     if (m_allDescendantsMightBeInvalid)