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

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/html/TextControlElement.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Text.h"
 #include "core/editing/FrameSelection.h"
 #include "core/editing/Position.h"
@@ skipping 192 matching lines @@
 TEST_F(TextControlElementTest, IndexForPosition) {
   HTMLInputElement* input =
       toHTMLInputElement(document().getElementById("input"));
   input->setValue("Hello");
   HTMLElement* innerEditor = input->innerEditorElement();
   EXPECT_EQ(5, TextControlElement::indexForPosition(
                    innerEditor,
                    Position(innerEditor, PositionAnchorType::AfterAnchor)));
 }
 
+TEST_F(TextControlElementTest, EnclosingTextControl) {
+  textControl().setValue("foobar");
+  EXPECT_EQ(nullptr, enclosingTextControl(Position(&document(), 0)));
+  EXPECT_EQ(nullptr, enclosingTextControl(Position(&textControl(), 0)));
+  EXPECT_EQ(&textControl(), enclosingTextControl(Position(
+                                textControl().innerEditorElement(), 0)));
+  EXPECT_EQ(&textControl(),
+            enclosingTextControl(
+                Position(textControl().innerEditorElement()->firstChild(), 0)));
+  EXPECT_EQ(nullptr,
+            enclosingTextControl(Position(textControl().innerEditorElement(),
+                                          PositionAnchorType::BeforeAnchor)));
+}
+
 }  // namespace blink