Fix update of validity cache value, so that it reflects the correct state of any FormControlElement.

Source/core/html/HTMLFormControlElement.cpp

Index: Source/core/html/HTMLFormControlElement.cpp
diff --git a/Source/core/html/HTMLFormControlElement.cpp b/Source/core/html/HTMLFormControlElement.cpp
index 7d15a19bcb726573a988af020ccc734aca3fa127..3ad09c1b9ffe14b63973f60877eb318aad4bf0be 100644
--- a/Source/core/html/HTMLFormControlElement.cpp
+++ b/Source/core/html/HTMLFormControlElement.cpp
@@ -58,6 +58,7 @@ HTMLFormControlElement::HTMLFormControlElement(const QualifiedName& tagName, Doc
     , m_willValidateInitialized(false)
     , m_willValidate(true)
     , m_isValid(true)
+    , m_validityIsDirty(true)
     , m_wasChangedSinceLastFormControlChangeEvent(false)
     , m_wasFocusedByMouse(false)
 {
@@ -473,20 +474,24 @@ bool HTMLFormControlElement::checkValidity(WillBeHeapVector<RefPtrWillBeMember<F
 
 bool HTMLFormControlElement::isValidFormControlElement()
 {
-    // If the following assertion fails, setNeedsValidityCheck() is not called
-    // correctly when something which changes validity is updated.
-    ASSERT(m_isValid == valid());
+    if (m_validityIsDirty) {
+        m_isValid = valid();
+        m_validityIsDirty = false;
+    } else {
+        // If the following assertion fails, setNeedsValidityCheck() is not called
+        // correctly when something which changes validity is updated.
+        ASSERT(m_isValid == valid());
+    }
     return m_isValid;
 }
 
 void HTMLFormControlElement::setNeedsValidityCheck()
 {
-    bool newIsValid = valid();
-    if (willValidate() && newIsValid != m_isValid) {
+    if (!m_validityIsDirty && willValidate()) {
         // Update style for pseudo classes such as :valid :invalid.
         setNeedsStyleRecalc(SubtreeStyleChange);
+        m_validityIsDirty = true;
     }
-    m_isValid = newIsValid;
 
     // Updates only if this control already has a validation message.
     if (isValidationMessageVisible()) {