Do not add features to classes in rightmost compound selector.

Source/core/css/RuleFeature.cpp

Index: Source/core/css/RuleFeature.cpp
diff --git a/Source/core/css/RuleFeature.cpp b/Source/core/css/RuleFeature.cpp
index 0d8cdffee98749c87216d7ebdc30b7e959a2cc89..43425064d661d16029fe93ad92047df16e67ffba 100644
--- a/Source/core/css/RuleFeature.cpp
+++ b/Source/core/css/RuleFeature.cpp
@@ -109,13 +109,16 @@ bool RuleFeatureSet::updateClassInvalidationSets(const CSSSelector& selector)
     AtomicString id;
     AtomicString tagName;
 
-    const CSSSelector* lastSelector = &selector;
-    for (; lastSelector->relation() == CSSSelector::SubSelector; lastSelector = lastSelector->tagHistory()) {
-        extractClassIdOrTag(*lastSelector, classes, id, tagName);
-    }
-    extractClassIdOrTag(*lastSelector, classes, id, tagName);
-
-    for (const CSSSelector* current = &selector ; current; current = current->tagHistory()) {
+    bool rightmostCompoundSelector = true;
+    for (const CSSSelector* current = &selector; current; current = current->tagHistory()) {
+        if (rightmostCompoundSelector) {
+            extractClassIdOrTag(*current, classes, id, tagName);
+            if (current->m_match == CSSSelector::Class)
+                ensureClassInvalidationSet(current->value());
+            if (current->relation() != CSSSelector::SubSelector)
+                rightmostCompoundSelector = false;
+            continue;

[esprehn, 2014/02/21 04:33:46]

I think you want to do this as two loops like before. The first loop is over the
right most compound selector.

[rune, 2014/02/21 10:17:17]

Done that now. I did a break on !SubSelector instead of duplicating the code for
extract* and ensure*. I do a null check on the selector pointer now. If you
think it's safe enough to assume the leftmost selector will always be a
descendant combinator flag, I can change back to not checking and add an assert
instead.

+        }
         if (current->m_match == CSSSelector::Class) {
             DescendantInvalidationSet& invalidationSet = ensureClassInvalidationSet(current->value());
             if (!id.isEmpty())