Simplify watched selector handling and remove remnants of user stylesheets

Source/core/css/resolver/MatchedPropertiesCache.cpp

Index: Source/core/css/resolver/MatchedPropertiesCache.cpp
diff --git a/Source/core/css/resolver/MatchedPropertiesCache.cpp b/Source/core/css/resolver/MatchedPropertiesCache.cpp
index 585d8dfaab029c1014871d0c2407b5abfe438586..75ecb2a37079ab3e2a1e958bcd6cd444ac40fadd 100644
--- a/Source/core/css/resolver/MatchedPropertiesCache.cpp
+++ b/Source/core/css/resolver/MatchedPropertiesCache.cpp
@@ -191,9 +191,6 @@ bool MatchedPropertiesCache::isCacheable(const Element* element, const RenderSty
         return false;
     if (style->hasCurrentColor())
         return false;
-    // CSSPropertyInternalCallback sets the rule's selector name into the RenderStyle, and that's not recalculated if the RenderStyle is loaded from the cache, so don't cache it.
-    if (!style->callbackSelectors().isEmpty())
-        return false;
     // The cache assumes static knowledge about which properties are inherited.
     if (parentStyle->hasExplicitlyInheritedProperties())
         return false;