Support invalidation sets for shadow combinators.

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 999f678ff48849045f26dfea9d7d516995adb74d..d49e8ad5c84db54ec5bd1b046881e124a9d161b7 100644
--- a/Source/core/css/RuleFeature.cpp
+++ b/Source/core/css/RuleFeature.cpp
@@ -122,10 +122,11 @@ RuleFeatureSet::InvalidationSetMode RuleFeatureSet::supportsClassDescendantInval
         } else if (!isSkippableComponentForInvalidation(*component)) {
             return foundDescendantRelation ? UseLocalStyleChange : UseSubtreeStyleChange;
         }
-        // FIXME: We can probably support ShadowAll and ShadowDeep.
         switch (component->relation()) {
         case CSSSelector::Descendant:
         case CSSSelector::Child:
+        case CSSSelector::Shadow:
+        case CSSSelector::ShadowDeep:
             foundDescendantRelation = true;
             // Fall through!
         case CSSSelector::SubSelector: