Count usage of :read-only and :read-write CSS selectors.

third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp

Index: third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp b/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
index 5b1effe33c5c5223cc379b57c484b80885f365fb..d2832746675a6d646508a768e0d27e24c3674349 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
@@ -60,6 +60,14 @@ static void recordSelectorStats(const CSSParserContext& context, const CSSSelect
                 if (context.mode() != UASheetMode)
                     feature = UseCounter::CSSSelectorInternalPseudoSpatialNavigationFocus;
                 break;
+            case CSSSelector::PseudoReadOnly:
+                if (context.mode() != UASheetMode)
+                    feature = UseCounter::CSSSelectorPseudoReadOnly;
+                break;
+            case CSSSelector::PseudoReadWrite:
+                if (context.mode() != UASheetMode)
+                    feature = UseCounter::CSSSelectorPseudoReadWrite;
+                break;
             default:
                 break;
             }