Do not dispatch 'change' events during pressing spin buttons for input[type=number].

Source/core/html/HTMLTextFormControlElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * 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
@@ skipping 165 matching lines @@
     setSelectionRange(selectionStart(), selectionEnd(), direction);
 }
 
 void HTMLTextFormControlElement::select()
 {
     setSelectionRange(0, numeric_limits<int>::max(), SelectionHasNoDirection);
 }
 
 void HTMLTextFormControlElement::dispatchFormControlChangeEvent()
 {
-    if (m_textAsOfLastFormControlChangeEvent != value()) {
+    if (!equalIgnoringNullity(m_textAsOfLastFormControlChangeEvent, value())) {
         dispatchChangeEvent();
         setTextAsOfLastFormControlChangeEvent(value());
     }
     setChangedSinceLastFormControlChangeEvent(false);
 }
 
 static inline bool hasVisibleTextArea(RenderObject* renderer, HTMLElement* innerText)
 {
     ASSERT(renderer);
     return renderer->style()->visibility() != HIDDEN && innerText && innerText->renderer() && innerText->renderBox()->height();
@@ skipping 449 matching lines @@
 
     return "ltr";
 }
 
 HTMLElement* HTMLTextFormControlElement::innerTextElement() const
 {
     return toHTMLElement(userAgentShadowRoot()->getElementById(ShadowElementNames::innerEditor()));
 }
 
 } // namespace Webcore