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

Source/core/rendering/RenderTextControlSingleLine.cpp

 /**
  * Copyright (C) 2006, 2007, 2010 Apple Inc. All rights reserved.
  *           (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * 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.
@@ skipping 29 matching lines @@
 
 namespace WebCore {
 
 using namespace HTMLNames;
 
 RenderTextControlSingleLine::RenderTextControlSingleLine(HTMLInputElement* element)
     : RenderTextControl(element)
     , m_shouldDrawCapsLockIndicator(false)
     , m_desiredInnerTextLogicalHeight(-1)
 {
-    ASSERT(element->hasTagName(inputTag));
 }
 
 RenderTextControlSingleLine::~RenderTextControlSingleLine()
 {
 }
 
 inline Element* RenderTextControlSingleLine::containerElement() const
 {
     return inputElement()->userAgentShadowRoot()->getElementById(ShadowElementNames::textFieldContainer());
 }
@@ skipping 374 matching lines @@
     if (innerTextElement())
         innerTextElement()->setScrollTop(newTop);
 }
 
 HTMLInputElement* RenderTextControlSingleLine::inputElement() const
 {
     return toHTMLInputElement(node());
 }
 
 }