[DMC #4] Add CompositionMarkerListImpl

third_party/WebKit/Source/core/editing/markers/CompositionMarkerListImpl.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 CompositionMarkerListImpl_h
+#define CompositionMarkerListImpl_h
+
+#include "core/editing/markers/DocumentMarkerList.h"
+
+namespace blink {
+
+// Implementation of DocumentMarkerList for Composition markers.
+// Markers are kept sorted by start offset, under the assumption that
+// Composition markers are typically inserted in an order.

[Xiaocheng, 2017/04/26 14:17:53]

Is MoveMarkers() the only site making out-of-order insertions?

It seems to be a little bit weird by stating an assumption without any
utilization/heuristic.

[rlanday, 2017/04/26 20:33:24]

The implication is supposed to be that we can keep the list sorted (to
perform certain operations more efficiently), while incurring hardly any
extra cost on inserts, since we're just going to be doing O(1) inserts
at the end of the list (the MoveMarkers() case is the only exception I
know of). I can try to make the comment more clear.

+class CORE_EXPORT CompositionMarkerListImpl : public DocumentMarkerList {

[Xiaocheng, 2017/04/26 14:17:53]

nit: final

+ public:
+  CompositionMarkerListImpl() = default;
+
+  // DocumentMarkerList implementations
+  bool IsEmpty() const final;
+
+  void Add(DocumentMarker*) final;
+  void Clear() final;
+
+  const HeapVector<Member<RenderedDocumentMarker>>& GetMarkers() const final;
+
+  bool MoveMarkers(int length, DocumentMarkerList* dst_list) final;
+  bool RemoveMarkers(unsigned start_offset, int length) final;
+  bool ShiftMarkers(unsigned offset,
+                    unsigned old_length,
+                    unsigned new_length) final;
+  DECLARE_TRACE();
+
+ private:
+  HeapVector<Member<RenderedDocumentMarker>> markers_;
+
+  DISALLOW_COPY_AND_ASSIGN(CompositionMarkerListImpl);
+};
+
+}  // namespace blink
+
+#endif  // CompositionMarkerListImpl_h