Add UseCounter for web components related CSS selectors

Source/core/css/parser/BisonCSSParser-in.cpp

Index: Source/core/css/parser/BisonCSSParser-in.cpp
diff --git a/Source/core/css/parser/BisonCSSParser-in.cpp b/Source/core/css/parser/BisonCSSParser-in.cpp
index d1b1f92b29efc92d2ada5787aeeea6288682e3ef..37b8a723d1b0bca4f4af125b78eb1cb72bc9dade 100644
--- a/Source/core/css/parser/BisonCSSParser-in.cpp
+++ b/Source/core/css/parser/BisonCSSParser-in.cpp
@@ -1757,6 +1757,45 @@ StyleRuleKeyframes* BisonCSSParser::createKeyframesRule(const String& name, Pass
     return rulePtr;
 }
 
+static void recordSelectorStats(const CSSParserContext& context, const CSSSelectorList& selectorList)
+{
+    if (!context.useCounter())
+        return;
+
+    for (const CSSSelector* selector = selectorList.first(); selector; selector = CSSSelectorList::next(*selector)) {
+        for ( ; ; selector = selector->tagHistory()) {
+            UseCounter::Feature feature = UseCounter::NumberOfFeatures;
+            switch (selector->pseudoType()) {
+            case CSSSelector::PseudoUnresolved:
+                feature = UseCounter::CSSSelectorPseudoUnresolved;
+                break;
+            case CSSSelector::PseudoShadow:
+                feature = UseCounter::CSSSelectorPseudoShadow;
+                break;
+            case CSSSelector::PseudoContent:
+                feature = UseCounter::CSSSelectorPseudoContent;
+                break;
+            case CSSSelector::PseudoHost:
+                feature = UseCounter::CSSSelectorPseudoHost;
+                break;
+            case CSSSelector::PseudoHostContext:
+                feature = UseCounter::CSSSelectorPseudoHostContext;
+                break;
+            default:
+                break;
+            }
+            if (feature != UseCounter::NumberOfFeatures)
+                context.useCounter()->count(feature);
+            if (selector->relation() == CSSSelector::ShadowDeep)

[kochi, 2014/06/18 09:03:31]

I noticed that some pseudo element can be combined with /deep/, separated the
recording point of /deep/ from
other pseudo selectors.

+                context.useCounter()->count(UseCounter::CSSDeepCombinator);
+            if (selector->selectorList())
+                recordSelectorStats(context, *selector->selectorList());
+            if (selector->isLastInTagHistory())

[esprehn, 2014/06/18 11:13:25]

I don't think you should need this check and break, shouldn't tagHistory() just
return null next and then your loop stops?

[kochi, 2014/06/18 16:30:23]

This was unintentionally tricky...
The |selector| was used for both inner and outer loop.

Once |selector| gets 0 at the end of tagHistory and exits the inner loop,
the outer loop still tries to continue to the next in CSSSelectorList,
but CSSSelectorList::next(*selector) steps on a null pointer.
As long as I read CSSSelectorList::next() correctly, at LastInTagHistory
the selector's next is handled correctly - so breaking here at LastInTagHistory
should make sense.

The logic should be correct, but I admit it is very confusing.
Fixed the code for readability.

+                break;
+        }
+    }
+}
+
 StyleRuleBase* BisonCSSParser::createStyleRule(Vector<OwnPtr<CSSParserSelector> >* selectors)
 {
     StyleRule* result = 0;
@@ -1767,6 +1806,7 @@ StyleRuleBase* BisonCSSParser::createStyleRule(Vector<OwnPtr<CSSParserSelector>
         rule->setProperties(createStylePropertySet());
         result = rule.get();
         m_parsedRules.append(rule.release());
+        recordSelectorStats(m_context, result->selectorList());
     }
     clearProperties();
     return result;