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

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

Index: third_party/WebKit/Source/core/html/TextControlElementTest.cpp
diff --git a/third_party/WebKit/Source/core/html/TextControlElementTest.cpp b/third_party/WebKit/Source/core/html/TextControlElementTest.cpp
index e5d47c5b0a5527c0f4dcb44c3b801cd491da3235..2b996cb0de19414a9418a7c4d2d68c757d255428 100644
--- a/third_party/WebKit/Source/core/html/TextControlElementTest.cpp
+++ b/third_party/WebKit/Source/core/html/TextControlElementTest.cpp
@@ -210,4 +210,18 @@ TEST_F(TextControlElementTest, IndexForPosition) {
                    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