Bug 1358448 - Add radio back to a radio group after moving out of a form. r=smaug

The container of a radio group is the form, if it belongs to a form, or the
document object otherwise.
When moving a radio out of a form, we should add it back to a radio group.
Similary, before moving the radio to a form, we should remove it from the
original radio group.

MozReview-Commit-ID: 22WsEhz2SXH

dom/html/HTMLFormElement.cpp

@@ -386,7 +386,7 @@ CollectOrphans(nsINode* aRemovalRoot,
     if (node->HasFlag(MAYBE_ORPHAN_FORM_ELEMENT)) {
       node->UnsetFlags(MAYBE_ORPHAN_FORM_ELEMENT);
       if (!nsContentUtils::ContentIsDescendantOf(node, aRemovalRoot)) {
-        node->ClearForm(true);
+        node->ClearForm(true, false);
 
         // When a form control loses its form owner, its state can change.
         node->UpdateState(true);