[Editing] Use VisiblePosition stardOfWord for textarea in spell checker.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * 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
@@ skipping 852 matching lines @@
          !position.anchorNode()->ownerShadowHost() ||
          (position.anchorNode()->parentNode() &&
           position.anchorNode()->parentNode()->isShadowRoot()));
   return enclosingTextControl(position.computeContainerNode());
 }
 
 TextControlElement* enclosingTextControl(Node* container) {
   if (!container)
     return nullptr;
   Element* ancestor = container->ownerShadowHost();
-  return ancestor && isTextControlElement(*ancestor) &&
-                 container->containingShadowRoot()->type() ==
-                     ShadowRootType::UserAgent
-             ? toTextControlElement(ancestor)
-             : 0;
+
+  if (!ancestor || !isTextControlElement(*ancestor))
+    return nullptr;
+
+  // textarea.shadowRoot is considered not enclosed.
+  if (container->isShadowRoot() &&
+      toShadowRoot(container)->type() == ShadowRootType::UserAgent &&
+      &toShadowRoot(container)->host() == ancestor)
+    return nullptr;
+
+  if (container->containingShadowRoot()->type() != ShadowRootType::UserAgent)
+    return nullptr;
+
+  return toTextControlElement(ancestor);
 }
 
 String TextControlElement::directionForFormData() const {
   for (const HTMLElement* element = this; element;
        element = Traversal<HTMLElement>::firstAncestor(*element)) {
     const AtomicString& dirAttributeValue = element->fastGetAttribute(dirAttr);
     if (dirAttributeValue.isNull())
       continue;
 
     if (equalIgnoringCase(dirAttributeValue, "rtl") ||
@@ skipping 277 matching lines @@
 
 void TextControlElement::copyNonAttributePropertiesFromElement(
     const Element& source) {
   const TextControlElement& sourceElement =
       static_cast<const TextControlElement&>(source);
   m_lastChangeWasUserEdit = sourceElement.m_lastChangeWasUserEdit;
   HTMLFormControlElement::copyNonAttributePropertiesFromElement(source);
 }
 
 }  // namespace blink