Clicking a button on disconnected form should not fire submit event.

third_party/WebKit/Source/core/html/HTMLButtonElement.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, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 87 matching lines @@
     if (formOwner() && isConnected())
       formOwner()->InvalidateDefaultButtonStyle();
   } else {
     if (params.name == formactionAttr)
       LogUpdateAttributeIfIsolatedWorldAndInDocument("button", params);
     HTMLFormControlElement::ParseAttribute(params);
   }
 }
 
 void HTMLButtonElement::DefaultEventHandler(Event* event) {
+  if (!isConnected())

[tkent, 2017/05/23 06:55:26]

Here is not a right place to check this.
We have a similar issue with <input type=submit>.

HTMLFormElement::PrepareForSubmission() is the right place, I think.

[Shanmuga Pandi, 2017/05/23 10:34:04]

Done.

+    return;
+
   if (event->type() == EventTypeNames::DOMActivate &&
       !IsDisabledFormControl()) {
     if (Form() && type_ == SUBMIT) {
       Form()->PrepareForSubmission(event, this);
       event->SetDefaultHandled();
     }
     if (Form() && type_ == RESET) {
       Form()->reset();
       event->SetDefaultHandled();
     }
@@ skipping 91 matching lines @@
 Node::InsertionNotificationRequest HTMLButtonElement::InsertedInto(
     ContainerNode* insertion_point) {
   InsertionNotificationRequest request =
       HTMLFormControlElement::InsertedInto(insertion_point);
   LogAddElementIfIsolatedWorldAndInDocument("button", typeAttr, formmethodAttr,
                                             formactionAttr);
   return request;
 }
 
 }  // namespace blink