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

third_party/WebKit/Source/core/editing/markers/CompositionMarker.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 CompositionMarker_h
 #define CompositionMarker_h
 
 #include "core/editing/markers/DocumentMarker.h"
 
 namespace blink {
 
 // A subclass of DocumentMarker used to store information specific to
 // composition markers. We store what color to display the underline (possibly
 // transparent), whether the underline should be thick or not, and what
 // background color should be used under the marked text (also possibly
 // transparent).
 class CORE_EXPORT CompositionMarker final : public DocumentMarker {
  public:
   CompositionMarker(unsigned start_offset,
                     unsigned end_offset,
                     Color underline_color,
                     bool thick,
                     Color background_color);
 
+  // DocumentMarker implementations
+  MarkerType GetType() const final;
+
+  // CompositionMarker-specific
   Color UnderlineColor() const;
   bool Thick() const;
   Color BackgroundColor() const;
 
  private:
   const Color underline_color_;
   const Color background_color_;
   const bool thick_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositionMarker);
 };
 
 DEFINE_TYPE_CASTS(CompositionMarker,
                   DocumentMarker,
                   marker,
                   marker->GetType() == DocumentMarker::kComposition,
                   marker.GetType() == DocumentMarker::kComposition);
 
 }  // namespace blink
 
 #endif