Only 'form associated' elements have a potential form owner.

Source/core/html/HTMLTextAreaElement.idl

 /*
  * Copyright (C) 2006, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2011 Motorola Mobility, Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 interface HTMLTextAreaElement : HTMLElement {
     [Reflect] attribute boolean autofocus;
     attribute long cols;
     [Reflect] attribute DOMString dirName;
     [Reflect] attribute boolean disabled;
-    readonly attribute HTMLFormElement form;
+    [ImplementedAs=formOwner] readonly attribute HTMLFormElement form;
     [RaisesException=Setter] attribute long maxLength;
     [Reflect] attribute DOMString name;
     [Reflect] attribute DOMString placeholder;
     [Reflect] attribute boolean readOnly;
     [Reflect] attribute boolean required;
     attribute long rows;
     [Reflect] attribute DOMString wrap;
     [RuntimeEnabled=InputModeAttribute, Reflect] attribute DOMString inputMode;
 
     readonly attribute DOMString type;
@@ skipping 17 matching lines @@
     [RaisesException] void setRangeText(DOMString replacement);
     [RaisesException] void setRangeText(DOMString replacement,
                         unsigned long start,
                         unsigned long end,
                         [Default=NullString] optional DOMString selectionMode);
 
     void setSelectionRange([Default=Undefined] optional long start,
                            [Default=Undefined] optional long end,
                            optional DOMString direction);
 };