Add UseCounter for web components related CSS selectors

This CL adds histogram statistics for the following
web components-related CSS selectors.

- :unresolved pseudo-class (for custom element)
- ::shadow pseudo element
- ::content pseudo element
- :host pseudo class
- :host-context() pseudo class
- /deep/ combinator

BUG=383749
TEST=open http://jsbin.com/bopezaso/2/edit, reload several times and see if FeatureObserver in chrome://histograms reflects it (number 465-470)

Review URL: https://codereview.chromium.org/339563004

git-svn-id: svn://svn.chromium.org/blink/trunk@176473 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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

@@ -1756,6 +1756,43 @@ 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 (const CSSSelector* current = selector; current ; current = current->tagHistory()) {
+            UseCounter::Feature feature = UseCounter::NumberOfFeatures;
+            switch (current->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 (current->relation() == CSSSelector::ShadowDeep)
+                context.useCounter()->count(UseCounter::CSSDeepCombinator);
+            if (current->selectorList())
+                recordSelectorStats(context, *current->selectorList());
+        }
+    }
+}
+
 StyleRuleBase* BisonCSSParser::createStyleRule(Vector<OwnPtr<CSSParserSelector> >* selectors)
 {
     StyleRule* result = 0;
@@ -1766,6 +1803,7 @@ 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;

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -463,6 +463,12 @@ public:
         HTMLImportsAsyncAttribute = 463,
         FontFaceSetReady = 464,
         XMLHttpRequestSynchronous = 465,
+        CSSSelectorPseudoUnresolved = 466,
+        CSSSelectorPseudoShadow = 467,
+        CSSSelectorPseudoContent = 468,
+        CSSSelectorPseudoHost = 469,
+        CSSSelectorPseudoHostContext = 470,
+        CSSDeepCombinator = 471,
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.
         // Also, run update_use_counter_feature_enum.py in chromium/src/tools/metrics/histograms/