[DMC #24] Add SpellingMarker and GrammarMarker (subclasses of DocumentMarker)

third_party/WebKit/Source/core/editing/markers/SpellCheckMarker.cpp

+// Copyright 2017 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/editing/markers/SpellCheckMarker.h"
+
+namespace blink {
+
+SpellCheckMarker::SpellCheckMarker(DocumentMarker::MarkerType type,
+                                   unsigned start_offset,
+                                   unsigned end_offset,
+                                   const String& description)
+    : DocumentMarker(type, start_offset, end_offset),
+      description_(description) {}

[yosin_UTC9, 2017/05/29 05:13:48]

Let's add DCHECK_LT(start_offset_, end_offset_)

+
+const String& SpellCheckMarker::Description() const {
+  return description_;
+}
+
+}  // namespace blink