Use new is*Element() helper functions more in editing code

Source/core/editing/SpellChecker.cpp

Index: Source/core/editing/SpellChecker.cpp
diff --git a/Source/core/editing/SpellChecker.cpp b/Source/core/editing/SpellChecker.cpp
index 3f8cb4bb921b158d01dda6bf1a8bbd3095634c75..770ce9307d52dffff2280cf3f290ceaf1eaa96ca 100644
--- a/Source/core/editing/SpellChecker.cpp
+++ b/Source/core/editing/SpellChecker.cpp
@@ -55,7 +55,7 @@ namespace {
 bool isSelectionInTextField(const VisibleSelection& selection)
 {
     HTMLTextFormControlElement* textControl = enclosingTextFormControl(selection.start());
-    return textControl && textControl->hasTagName(inputTag) && toHTMLInputElement(textControl)->isTextField();
+    return isHTMLInputElement(textControl) && toHTMLInputElement(textControl)->isTextField();
 }
 
 } // namespace
@@ -128,7 +128,7 @@ void SpellChecker::didBeginEditing(Element* element)
             HTMLTextFormControlElement* textControl = toHTMLTextFormControlElement(element);
             parent = textControl;
             element = textControl->innerTextElement();
-            isTextField = textControl->hasTagName(inputTag) && toHTMLInputElement(textControl)->isTextField();
+            isTextField = isHTMLInputElement(*textControl) && toHTMLInputElement(*textControl).isTextField();
         }
 
         if (isTextField || !parent->isAlreadySpellChecked()) {