[DMC #25] Make DocumentMarker::GetType() virtual

third_party/WebKit/Source/core/editing/markers/GrammarMarker.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/GrammarMarker.h"
 
 namespace blink {
 
 GrammarMarker::GrammarMarker(unsigned start_offset,
                              unsigned end_offset,
                              const String& description)
-    : SpellCheckMarker(DocumentMarker::kGrammar,
-                       start_offset,
-                       end_offset,
-                       description) {}
+    : SpellCheckMarker(start_offset, end_offset, description) {}
+
+DocumentMarker::MarkerType GrammarMarker::GetType() const {
+  return DocumentMarker::kGrammar;
+}
 
 }  // namespace blink