Introduce toHTMLInputElement(Node*), and use it.

Source/core/html/shadow/TextFieldDecorationElement.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 106 matching lines @@
     toHTMLElement(existingRoot->firstChild())->setInlineStyleProperty(CSSPropertyWebkitFlexGrow, 1.0, CSSPrimitiveValue::CSS_NUMBER);
     box->appendChild(HTMLShadowElement::create(HTMLNames::shadowTag, input->document()));
     setInlineStyleProperty(CSSPropertyDisplay, visible ? CSSValueBlock : CSSValueNone);
     box->appendChild(this);
 }
 
 inline HTMLInputElement* TextFieldDecorationElement::hostInput()
 {
     // TextFieldDecorationElement is created only by C++ code, and it is always
     // in <input> shadow.
-    ASSERT_WITH_SECURITY_IMPLICATION(!shadowHost() || shadowHost()->hasTagName(inputTag));
-    return static_cast<HTMLInputElement*>(shadowHost());
+    return toHTMLInputElement(shadowHost());
 }
 
 bool TextFieldDecorationElement::isTextFieldDecoration() const
 {
     return true;
 }
 
 void TextFieldDecorationElement::updateImage()
 {
     if (!renderer() || !renderer()->isImage())
@@ skipping 89 matching lines @@
 bool TextFieldDecorationElement::willRespondToMouseClickEvents()
 {
     const HTMLInputElement* input = hostInput();
     if (!input->isDisabledOrReadOnly())
         return true;
 
     return HTMLDivElement::willRespondToMouseClickEvents();
 }
 
 } // namespace WebCore