Add CompositionMarkerList in preparation for DocumentMarkerController refactor

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

 /*
  * This file is part of the DOM implementation for WebCore.
  *
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 143 matching lines @@
   const String& description() const;
   bool activeMatch() const;
   Color underlineColor() const;
   bool thick() const;
   Color backgroundColor() const;
   DocumentMarkerDetails* details() const;
 
   void setActiveMatch(bool);
   void clearDetails() { m_details.clear(); }
 
-  // Offset modifications are done by DocumentMarkerController.
-  // Other classes should not call following setters.
+  struct ShiftMarkerResult {
+    unsigned newStartOffset;
+    unsigned newEndOffset;
+    bool shouldRemoveMarker;
+  };
+
+  ShiftMarkerResult getShiftedMarkerPosition(unsigned offset,

[Xiaocheng, 2017/03/25 00:05:35]

I think we should add unit test for this function.

Then unit tests for DML::shiftMarkers can be simplified:
1. Verify return value when nothing is modified
2. Verify return value and resulting list when a marker is modified
3. Verify return value and resulting list when a marker is removed

+                                             unsigned oldLength,
+                                             unsigned newLength) const;
+
+  // Offset modifications are done by DocumentMarkerController and subclasses of
+  // DocumentMarkerList. Other classes should not call following setters.
   void setStartOffset(unsigned offset) { m_startOffset = offset; }
   void setEndOffset(unsigned offset) { m_endOffset = offset; }
   void shiftOffsets(int delta);
 
   bool operator==(const DocumentMarker& o) const {
     return type() == o.type() && startOffset() == o.startOffset() &&
            endOffset() == o.endOffset();
   }
 
   bool operator!=(const DocumentMarker& o) const { return !(*this == o); }
@@ skipping 21 matching lines @@
   virtual bool isDescription() const { return false; }
   virtual bool isTextMatch() const { return false; }
   virtual bool isComposition() const { return false; }
 
   DEFINE_INLINE_VIRTUAL_TRACE() {}
 };
 
 }  // namespace blink
 
 #endif  // DocumentMarker_h