Add CompositionMarkerList in preparation for DocumentMarkerController refactor

third_party/WebKit/Source/core/editing/markers/CompositionMarkerList.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 CompositionMarkerList_h
+#define CompositionMarkerList_h
+
+#include "core/editing/markers/EditingMarkerList.h"
+
+namespace blink {
+
+class CORE_EXPORT CompositionMarkerList final : public EditingMarkerList {
+ public:
+  CompositionMarkerList();
+
+  DocumentMarker::MarkerType allowedMarkerType() const final;
+
+  DISALLOW_COPY_AND_ASSIGN(CompositionMarkerList);
+};
+
+}  // namespace blink
+
+#endif  // CompositionMarkerList_h