Introduce toHTMLInputElement(Node*), and use it.

Source/core/loader/FormSubmission.cpp

Index: Source/core/loader/FormSubmission.cpp
diff --git a/Source/core/loader/FormSubmission.cpp b/Source/core/loader/FormSubmission.cpp
index 7407bef9440d0f35fc8b4fefee2962c594d493e7..22bc20c5a715bb03280902e2c7bac10dd52d87cc 100644
--- a/Source/core/loader/FormSubmission.cpp
+++ b/Source/core/loader/FormSubmission.cpp
@@ -186,8 +186,8 @@ PassRefPtr<FormSubmission> FormSubmission::create(HTMLFormElement* form, const A
         HTMLElement* element = toHTMLElement(control);
         if (!element->isDisabledFormControl())
             control->appendFormData(*domFormData, isMultiPartForm);
-        if (element->hasLocalName(inputTag)) {
-            HTMLInputElement* input = static_cast<HTMLInputElement*>(control);
+        if (element->hasTagName(inputTag)) {
+            HTMLInputElement* input = toHTMLInputElement(element);
             if (input->isTextField())
                 formValues.append(pair<String, String>(input->name().string(), input->value()));
             if (input->isPasswordField() && !input->value().isEmpty())