Add DocumentMarker::clone()

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

Index: third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
diff --git a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
index dbcfdf2964555be13aa50b7551bf2305f37a6fd8..b8260c3856eea6ac0aecfcb557dc46cdfe235e4e 100644
--- a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
+++ b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
@@ -145,7 +145,8 @@ class CORE_EXPORT DocumentMarker : public GarbageCollected<DocumentMarker> {
                  bool thick,
                  Color backgroundColor);
 
-  DocumentMarker(const DocumentMarker&);
+  DocumentMarker* cloneWithNewOffsets(unsigned startOffset,
+                                      unsigned endOffset) const;
 
   MarkerType type() const { return m_type; }
   unsigned startOffset() const { return m_startOffset; }
@@ -176,6 +177,10 @@ class CORE_EXPORT DocumentMarker : public GarbageCollected<DocumentMarker> {
 
   DECLARE_TRACE();
 
+ protected:
+  DocumentMarker(const DocumentMarker&);
+  virtual DocumentMarker* clone() const;
+
  private:
   MarkerType m_type;
   unsigned m_startOffset;