Support invalidation sets for :host pseudo.

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 d49e8ad5c84db54ec5bd1b046881e124a9d161b7..eb6055eedeeed2116ef73b6c78d0fdfebb494d1c 100644
--- a/Source/core/css/RuleFeature.cpp
+++ b/Source/core/css/RuleFeature.cpp
@@ -54,7 +54,7 @@ static bool isSkippableComponentForInvalidation(const CSSSelector& selector)
         || selector.isAttributeSelector())
         return true;
     if (selector.m_match == CSSSelector::PseudoElement) {
-        switch (selector.m_pseudoType) {
+        switch (selector.pseudoType()) {
         case CSSSelector::PseudoBefore:
         case CSSSelector::PseudoAfter:
         case CSSSelector::PseudoBackdrop:
@@ -119,6 +119,16 @@ RuleFeatureSet::InvalidationSetMode RuleFeatureSet::supportsClassDescendantInval
         if (component->m_match == CSSSelector::Class) {
             if (!foundDescendantRelation)
                 foundIdent = true;
+        } else if (component->pseudoType() == CSSSelector::PseudoHost) {
+            const CSSSelectorList* list = component->selectorList();
+            if (list) {

[ojan, 2014/03/22 00:32:23]

Nit: typically we write this as follows: 
if (const CSSSelectorList* list = component->selectorList()) {

In addition to being one line, it has the advantage of scoping the variable to
the contents of the if-statement.

+                ASSERT(list->hasOneSelector());

[esprehn, 2014/03/22 01:25:34]

Why does this have to have one selector? You can write host(a, b)

+                InvalidationSetMode hostMode = supportsClassDescendantInvalidation(*list->first());
+                if (hostMode == UseSubtreeStyleChange)
+                    return foundDescendantRelation ? UseLocalStyleChange : UseSubtreeStyleChange;
+                if (hostMode == AddFeatures)
+                    foundIdent = true;
+            }
         } else if (!isSkippableComponentForInvalidation(*component)) {
             return foundDescendantRelation ? UseLocalStyleChange : UseSubtreeStyleChange;
         }
@@ -163,19 +173,37 @@ RuleFeatureSet::InvalidationSetMode RuleFeatureSet::updateClassInvalidationSets(
     AtomicString id;
     AtomicString tagName;
 
+    const CSSSelector* current = extractInvalidationSetFeatures(selector, classes, id, tagName);
+    if (!current || !(current = current->tagHistory()))

[ojan, 2014/03/22 00:32:23]

Nit: In contrast to the above case, I find setting current inside the
if-statement confusing. It looks like a typo. I can see that it's not by
inspecting the code closely.

The difference with the above case IMO is the type. The type means it would be a
compiler error if you change the = to an ==.

[esprehn, 2014/03/22 01:25:34]

Don't do assignments inside || or &&

+        return AddFeatures;
+
+    addFeaturesToInvalidationSets(*current, classes, id, tagName);
+    return AddFeatures;
+}
+
+const CSSSelector* RuleFeatureSet::extractInvalidationSetFeatures(const CSSSelector& selector, Vector<AtomicString>& classes, AtomicString& id, AtomicString& tagName)
+{
     const CSSSelector* lastSelector = &selector;
     for (; lastSelector; lastSelector = lastSelector->tagHistory()) {
         extractClassIdOrTag(*lastSelector, classes, id, tagName);
-        if (lastSelector->m_match == CSSSelector::Class)
+        if (lastSelector->m_match == CSSSelector::Class) {
             ensureClassInvalidationSet(lastSelector->value());
+        } else if (lastSelector->pseudoType() == CSSSelector::PseudoHost) {
+            const CSSSelectorList* list = lastSelector->selectorList();
+            if (list)

[ojan, 2014/03/22 00:32:23]

Ditto first comment.

+                extractInvalidationSetFeatures(*list->first(), classes, id, tagName);
+        }
+
         if (lastSelector->relation() != CSSSelector::SubSelector)
             break;
     }
+    return lastSelector;
+}
 
-    if (!lastSelector)
-        return AddFeatures;
-
-    for (const CSSSelector* current = lastSelector->tagHistory(); current; current = current->tagHistory()) {
+void RuleFeatureSet::addFeaturesToInvalidationSets(const CSSSelector& selector, const Vector<AtomicString>& classes, AtomicString id, AtomicString tagName)
+{
+    const CSSSelector* current = &selector;
+    for (; current; current = current->tagHistory()) {
         if (current->m_match == CSSSelector::Class) {
             DescendantInvalidationSet& invalidationSet = ensureClassInvalidationSet(current->value());
             if (!id.isEmpty())
@@ -185,9 +213,11 @@ RuleFeatureSet::InvalidationSetMode RuleFeatureSet::updateClassInvalidationSets(
             for (Vector<AtomicString>::const_iterator it = classes.begin(); it != classes.end(); ++it) {
                 invalidationSet.addClass(*it);
             }
+        } else if (current->pseudoType() == CSSSelector::PseudoHost) {
+            if  (current->selectorList())

[ojan, 2014/03/22 00:32:23]

Nit: extra space after the if.

+                addFeaturesToInvalidationSets(*current->selectorList()->first(), classes, id, tagName);
         }
     }
-    return AddFeatures;
 }
 
 void RuleFeatureSet::addAttributeInASelector(const AtomicString& attributeName)