Add DocumentMarker::clone()

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

Index: third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.h
diff --git a/third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.h b/third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.h
index 6e2803cf357f4b570a58f50941320ed79412b3b5..f22ea685d03d6738872b27530701cd044117aea5 100644
--- a/third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.h
+++ b/third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.h
@@ -41,6 +41,8 @@ class RenderedDocumentMarker final : public DocumentMarker {
     return new RenderedDocumentMarker(marker);
   }
 
+  RenderedDocumentMarker* clone() const final;
+
   bool isRendered() const { return m_state == State::ValidNotNull; }
   bool contains(const LayoutPoint& point) const {
     DCHECK_EQ(m_state, State::ValidNotNull);
@@ -67,6 +69,9 @@ class RenderedDocumentMarker final : public DocumentMarker {
   void invalidate() { m_state = State::Invalid; }
   bool isValid() const { return m_state != State::Invalid; }
 
+ protected:
+  RenderedDocumentMarker(RenderedDocumentMarker&) = default;
+
  private:
   explicit RenderedDocumentMarker(const DocumentMarker& marker)
       : DocumentMarker(marker), m_state(State::Invalid) {}