Introduce toHTMLInputElement(Node*), and use it.

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 9e433c04d01fcc617e9b16704afa25929a0560ee..633d4b9a15736ef180928eba707270253b8b0752 100644
--- a/Source/core/html/HTMLFormElement.cpp
+++ b/Source/core/html/HTMLFormElement.cpp
@@ -310,10 +310,10 @@ void HTMLFormElement::getTextFieldValues(StringPairVector& fieldNamesAndValues)
     for (unsigned i = 0; i < m_associatedElements.size(); ++i) {
         FormAssociatedElement* control = m_associatedElements[i];
         HTMLElement* element = toHTMLElement(control);
-        if (!element->hasLocalName(inputTag))
+        if (!element->hasTagName(inputTag))
             continue;
 
-        HTMLInputElement* input = static_cast<HTMLInputElement*>(control);
+        HTMLInputElement* input = toHTMLInputElement(element);
         if (!input->isTextField())
             continue;