Revert of Simplify form validation handling

Source/core/html/HTMLFieldSetElement.cpp

Index: Source/core/html/HTMLFieldSetElement.cpp
diff --git a/Source/core/html/HTMLFieldSetElement.cpp b/Source/core/html/HTMLFieldSetElement.cpp
index 3342e44e7f3e5bd0baa9172958b6b90d1c6c39e4..90dcdd93ee02e5a02568ed56d383329e7377f530 100644
--- a/Source/core/html/HTMLFieldSetElement.cpp
+++ b/Source/core/html/HTMLFieldSetElement.cpp
@@ -76,6 +76,15 @@
     return true;
 }
 
+void HTMLFieldSetElement::setNeedsValidityCheck()
+{
+    // For now unconditionally order style recalculation, which triggers
+    // validity recalculation. In the near future, consider implement validity
+    // cache and recalculate style only if it changed.
+    pseudoStateChanged(CSSSelector::PseudoValid);
+    pseudoStateChanged(CSSSelector::PseudoInvalid);
+}
+
 void HTMLFieldSetElement::invalidateDisabledStateUnder(Element& base)
 {
     for (HTMLFormControlElement& element : Traversal<HTMLFormControlElement>::descendantsOf(base))