Fix bug where form/fieldset :valid/:invalid won't be recalculated upon control's willValidate change

Source/core/html/HTMLFormElement.cpp

Index: Source/core/html/HTMLFormElement.cpp
diff --git a/Source/core/html/HTMLFormElement.cpp b/Source/core/html/HTMLFormElement.cpp
index 6504dbf561d24d60aba8a1d4d529e6c5dc57f1bc..4ea622e713450da5cc45fe5381cca5395930cea4 100644
--- a/Source/core/html/HTMLFormElement.cpp
+++ b/Source/core/html/HTMLFormElement.cpp
@@ -77,6 +77,7 @@ HTMLFormElement::HTMLFormElement(Document& document)
     , m_shouldSubmit(false)
     , m_isInResetFunction(false)
     , m_wasDemoted(false)
+    , m_invalidControlsCount(0)
     , m_pendingAutocompleteEventsQueue(GenericEventQueue::create(this))
 {
 }
@@ -716,12 +717,27 @@ HTMLFormControlElement* HTMLFormElement::defaultButton() const
     return 0;
 }
 
-void HTMLFormElement::setNeedsValidityCheck()
-{
-    // For now unconditionally order style recalculation, which triggers
-    // validity recalculation. In the near future, implement validity cache and
-    // recalculate style only if it changed.
-    setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::createWithExtraData(StyleChangeReason::PseudoClass, StyleChangeExtraData::Invalid));
+void HTMLFormElement::setNeedsValidityCheck(ValidityRecalcReason reason, bool isValid)
+{
+    bool formWasInvalid = m_invalidControlsCount > 0;
+    switch (reason) {
+    case ElementRemoval:
+        if (!isValid)
+            --m_invalidControlsCount;
+        break;
+    case ElementAddition:
+        if (!isValid)
+            ++m_invalidControlsCount;
+        break;
+    case ElementModification:
+        if (isValid)
+            --m_invalidControlsCount;
+        else
+            ++m_invalidControlsCount;
+        break;
+    }
+    if (formWasInvalid != (m_invalidControlsCount > 0))
+        setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::createWithExtraData(StyleChangeReason::PseudoClass, StyleChangeExtraData::Invalid));
 }
 
 bool HTMLFormElement::checkValidity()
@@ -731,6 +747,9 @@ bool HTMLFormElement::checkValidity()
 
 bool HTMLFormElement::checkInvalidControlsAndCollectUnhandled(WillBeHeapVector<RefPtrWillBeMember<HTMLFormControlElement> >* unhandledInvalidControls, CheckValidityEventBehavior eventBehavior)
 {
+    if (!unhandledInvalidControls && eventBehavior == CheckValidityDispatchNoEvent)
+        return m_invalidControlsCount;
+
     RefPtrWillBeRawPtr<HTMLFormElement> protector(this);
     // Copy associatedElements because event handlers called from
     // HTMLFormControlElement::checkValidity() might change associatedElements.
@@ -739,15 +758,17 @@ bool HTMLFormElement::checkInvalidControlsAndCollectUnhandled(WillBeHeapVector<R
     elements.reserveCapacity(associatedElements.size());
     for (unsigned i = 0; i < associatedElements.size(); ++i)
         elements.append(associatedElements[i]);
-    bool hasInvalidControls = false;
+    int invalidControlsCount = 0;
     for (unsigned i = 0; i < elements.size(); ++i) {
         if (elements[i]->form() == this && elements[i]->isFormControlElement()) {
             HTMLFormControlElement* control = toHTMLFormControlElement(elements[i].get());
             if (!control->checkValidity(unhandledInvalidControls, eventBehavior) && control->formOwner() == this)
-                hasInvalidControls = true;
+                ++invalidControlsCount;
         }
     }
-    return hasInvalidControls;
+    if (eventBehavior == CheckValidityDispatchNoEvent)
+        ASSERT(invalidControlsCount == m_invalidControlsCount);
+    return invalidControlsCount;
 }
 
 bool HTMLFormElement::reportValidity()