[DMC #1.9] Move DocumentMarkerListEditor to its own .h/.cpp files

third_party/WebKit/Source/core/editing/markers/DocumentMarkerListEditor.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 DocumentMarkerListEditor_h
+#define DocumentMarkerListEditor_h
+
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class DocumentMarker;
+class RenderedDocumentMarker;
+
+class DocumentMarkerListEditor {
+ public:
+  using MarkerList = HeapVector<Member<RenderedDocumentMarker>>;
+
+  static void AddMarker(MarkerList*, const DocumentMarker*);
+
+  // Returns true if a marker was moved, false otherwise.
+  static bool MoveMarkers(MarkerList* src_list,
+                          int length,
+                          MarkerList* dst_list);
+
+  // Returns true if a marker was removed, false otherwise.
+  static bool RemoveMarkers(MarkerList*, unsigned start_offset, int length);
+
+  // Returns true if a marker was shifted or removed, false otherwise.
+  static bool ShiftMarkers(MarkerList*,
+                           unsigned offset,
+                           unsigned old_length,
+                           unsigned new_length);
+
+ private:
+  static void MergeOverlapping(MarkerList*, RenderedDocumentMarker* to_insert);
+};
+
+}  // namespace blink
+
+#endif  // DocumentMarkerListEditor_h