Fixed the behaviour of form submit to Firefox: form does not submit once it has been removed.

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 53b47e973450e2b06b2e9d55df92b5d233e12752..760b1adc9e0e36f73e07a62f863d3f53b2407d3b 100644
--- a/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
@@ -350,9 +350,11 @@ void HTMLFormElement::submit(Event* event, bool activateSubmitButton)
     LocalFrame* frame = document().frame();
     if (!view || !frame || !frame->page())
         return;
-    // See crbug.com/586749.
+
+    // Do not submit if the form is not attached to the document.
+    // This matches the behaviour in fireFox.

[iclelland, 2016/08/23 17:46:23]

Nit: "Firefox"

Also, you could put a reference to the bug here in case someone wants to see
context for the change.

[lunalu1, 2016/08/24 15:24:42]

Done.

     if (!isConnected())
-        UseCounter::count(document(), UseCounter::FormSubmissionNotInDocumentTree);
+        return;
 
     if (m_isSubmitting)
         return;