Non-activated default buttons prevent implicit form submission.

Source/core/html/HTMLInputElement.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, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
@@ skipping 790 matching lines @@
     // fall back to title attribute
     if (alt.isNull())
         alt = getAttribute(titleAttr);
     if (alt.isNull())
         alt = getAttribute(valueAttr);
     if (alt.isEmpty())
         alt = locale().queryString(blink::WebLocalizedString::InputElementAltText);
     return alt;
 }
 
-bool HTMLInputElement::isSuccessfulSubmitButton() const
+bool HTMLInputElement::canBeSuccessfulSubmitButton() const
 {
-    // HTML spec says that buttons must have names to be considered successful.
-    // However, other browsers do not impose this constraint. So we do not.
-    return !isDisabledFormControl() && m_inputType->canBeSuccessfulSubmitButton();
+    return m_inputType->canBeSuccessfulSubmitButton();
 }
 
 bool HTMLInputElement::isActivatedSubmit() const
 {
     return m_isActivatedSubmit;
 }
 
 void HTMLInputElement::setActivatedSubmit(bool flag)
 {
     m_isActivatedSubmit = flag;
@@ skipping 1034 matching lines @@
 }
 
 #if ENABLE(INPUT_MULTIPLE_FIELDS_UI)
 PassRefPtr<RenderStyle> HTMLInputElement::customStyleForRenderer()
 {
     return m_inputTypeView->customStyleForRenderer(originalStyleForRenderer());
 }
 #endif
 
 } // namespace