Add EditingMarkerList in preparation for DocumentMarkerController refactor

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

Index: third_party/WebKit/Source/core/editing/markers/EditingMarkerList.h
diff --git a/third_party/WebKit/Source/core/editing/markers/EditingMarkerList.h b/third_party/WebKit/Source/core/editing/markers/EditingMarkerList.h
new file mode 100644
index 0000000000000000000000000000000000000000..7560feaf4c228e4801baa3d51282cb5b18d58187
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/markers/EditingMarkerList.h
@@ -0,0 +1,50 @@
+// 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 EditingMarkerList_h
+#define EditingMarkerList_h
+
+#include "core/editing/markers/DocumentMarkerList.h"
+
+namespace blink {
+
+class DocumentMarker;
+
+// EditingMarkerList is a subclass of DocumentMarkerList that takes advantage of
+// the fact that its markers are sorted if they are inserted in a sorted order,
+// but also supports efficiently inserting markers in non-sorted order.
+// TODO(rlanday): Currently if markers are inserted in non-sorted order, this
+// class just leaves them non-sorted until the list is cleared; is it ever
+// advantageous to pre-emptively sort the list?
+class CORE_EXPORT EditingMarkerList : public DocumentMarkerList {
+ public:
+  EditingMarkerList();
+
+  // DocumentMarkerList implementations
+  bool isEditingMarkerList() const final;
+
+  void add(DocumentMarker*) override;
+  void clear() final;
+
+  DECLARE_VIRTUAL_TRACE();
+
+ protected:
+  // TODO(rlanday): determine if/when we should sort the marker list to improve
+  // performance
+  bool markerListIsSorted() const final;
+
+  bool m_markersAreSorted;
+
+  DISALLOW_COPY_AND_ASSIGN(EditingMarkerList);
+};
+
+DEFINE_TYPE_CASTS(EditingMarkerList,
+                  DocumentMarkerList,
+                  list,
+                  list->isEditingMarkerList(),
+                  list.isEditingMarkerList());
+
+}  // namespace blink
+
+#endif  // EditingMarkerList_h