Fixed the behaviour of form submit to match the standard: no submit is taken place when the form is detached from the document (e.g., form is removed).
One additional layout test (form-removed-from-document.html) is added to verify the change made above.
Two layout tests has been modified to match the behaviour of submitting form (when from is detached from/attached to the document) in Firefox.
BUG=
586749
Committed:
https://crrev.com/962c2a22ddc474255c776aefc7abeba00edc7470
Cr-Commit-Position: refs/heads/master@{#425734}