Introduce toHTMLInputElement(Node*), and use it.

Source/core/rendering/RenderButton.cpp

 /**
  * Copyright (C) 2005 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 91 matching lines @@
     // when the content overflows, treat it the same as align-items: flex-start.
     innerStyle->setMarginTop(Length());
     innerStyle->setMarginBottom(Length());
     innerStyle->setFlexDirection(style()->flexDirection());
 }
 
 void RenderButton::updateFromElement()
 {
     // If we're an input element, we may need to change our button text.
     if (node()->hasTagName(inputTag)) {
-        HTMLInputElement* input = static_cast<HTMLInputElement*>(node());
+        HTMLInputElement* input = toHTMLInputElement(node());
         String value = input->valueWithDefault();
         setText(value);
     }
 }
 
 void RenderButton::setText(const String& str)
 {
     if (str.isEmpty()) {
         if (m_buttonText) {
             m_buttonText->destroy();
@@ skipping 41 matching lines @@
         // baseline for the empty case manually here.
         if (direction == HorizontalLine)
             return marginTop() + borderTop() + paddingTop() + contentHeight();
 
         return marginRight() + borderRight() + paddingRight() + contentWidth();
     }
     return RenderFlexibleBox::baselinePosition(baseline, firstLine, direction, linePositionMode);
 }
 
 } // namespace WebCore