Introduce EditingUtilitiesTest.cpp as a home of nextPositionOf() test

Source/core/editing/EditingUtilitiesTest.cpp

+// Copyright 2015 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 "config.h"
+#include "core/editing/EditingUtilities.h"
+
+#include "core/editing/EditingTestBase.h"
+
+namespace blink {
+
+class EditingUtilitiesTest : public EditingTestBase {
+};
+
+TEST_F(EditingUtilitiesTest, NextNodeIndex)
+{
+    const char* bodyContent = "<p id='host'>00<b id='one'>11</b><b id='two'>22</b>33</p>";
+    const char* shadowContent = "<content select=#two></content><content select=#one></content>";
+    setBodyContent(bodyContent);
+    setShadowContent(shadowContent);
+    Node* host = document().getElementById("host");
+    Node* two = document().getElementById("two");
+
+    EXPECT_EQ(Position(host, 3), nextPositionOf(Position(two, 2), PositionMoveType::CodePoint));
+    EXPECT_EQ(PositionInComposedTree(host, 1), nextPositionOf(PositionInComposedTree(two, 2), PositionMoveType::CodePoint));
+}
+
+} // namespace blink