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

third_party/WebKit/Source/core/editing/markers/GrammarMarker.h

 // 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.
 
 #ifndef GrammarMarker_h
 #define GrammarMarker_h
 
 #include "core/editing/markers/SpellCheckMarker.h"
 
 namespace blink {
 
 // A subclass of DocumentMarker used to store information specific to grammar
 // markers. Spelling and grammar markers are identical except that they mark
 // either spelling or grammar errors, respectively, so nearly all functionality
 // is delegated to a common base class, SpellCheckMarker.
 class CORE_EXPORT GrammarMarker final : public SpellCheckMarker {
  public:
   GrammarMarker(unsigned start_offset,
                 unsigned end_offset,
                 const String& description);
 
  private:
+  // DocumentMarker implementations
+  MarkerType GetType() const final;
+
   DISALLOW_COPY_AND_ASSIGN(GrammarMarker);
 };
 
 }  // namespace blink
 
 #endif