Add DocumentMarkerList interface

third_party/WebKit/Source/core/editing/markers/DocumentMarkerList.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 DocumentMarkerList_h
+#define DocumentMarkerList_h
+
+#include "core/editing/markers/DocumentMarker.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class DocumentMarkerList
+    : public GarbageCollectedFinalized<DocumentMarkerList> {
+ public:
+  DocumentMarkerList();
+
+  virtual ~DocumentMarkerList();
+
+  virtual bool Empty() const = 0;
+
+  virtual void Add(DocumentMarker*) = 0;
+  virtual void Clear() = 0;
+
+  virtual void AppendMarkersToInputList(DocumentMarkerVector* list) const = 0;
+
+  // Returns true if at least one marker is copied, false otherwise

[Xiaocheng, 2017/04/12 00:30:51]

Please also document the behavior of this function, i.e., which markers will be
moved and how their offsets will be changed.

Ditto for the two other functions.

nit: s/copied/moved/

+  virtual bool MoveMarkers(int length, DocumentMarkerList* dst_list) = 0;
+
+  // Returns true if at least one marker is removed, false otherwise
+  virtual bool RemoveMarkers(unsigned start_offset, int length) = 0;
+
+  // Returns true if at least one marker is shifted or removed, false otherwise
+  virtual bool ShiftMarkers(unsigned offset,
+                            unsigned old_length,
+                            unsigned new_length) = 0;
+
+  DEFINE_INLINE_VIRTUAL_TRACE() {}
+  DISALLOW_COPY_AND_ASSIGN(DocumentMarkerList);
+};
+
+}  // namespace blink
+
+#endif  // DocumentMarkerList_h