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

third_party/WebKit/Source/core/html/HTMLFormElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLFormElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLFormElement.cpp b/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
index c7383329660c994d10e0b8fe301908d6b9c3fec5..92c2a5a4215b5958ebc3d1a59c66b4bb6b77f973 100644
--- a/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
@@ -283,7 +283,8 @@ void HTMLFormElement::PrepareForSubmission(
     Event* event,
     HTMLFormControlElement* submit_button) {
   LocalFrame* frame = GetDocument().GetFrame();
-  if (!frame || is_submitting_ || in_user_js_submit_event_)
+  if (!frame || is_submitting_ || in_user_js_submit_event_ ||
+      (submit_button && !submit_button->isConnected()))

[tkent, 2017/05/23 23:32:52]

You don't need to check isConnected() of submit_button. isConnected() for |this|
is enough because their connectedness is always same.
Please show a warning message same as HTMLFormElement::Submit().

Note that the isConnected() check in Submit() should be moved to here, but we
can't do it now because PrepareForSubmission() is not always called.

[Shanmuga Pandi, 2017/05/24 07:09:54]

Done.

     return;
 
   if (GetDocument().IsSandboxed(kSandboxForms)) {