Add DocumentMarker::clone()

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

Index: third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
diff --git a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
index b18b3fd88304206850783d3ee5de7a20483edd5f..722597baebdf25ea60f01e998b4248403e757554 100644
--- a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
+++ b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
@@ -129,6 +129,19 @@ inline TextCompositionMarkerDetails* toTextCompositionMarkerDetails(
   return nullptr;
 }
 
+DocumentMarker* DocumentMarker::clone() const {
+  return new DocumentMarker(*this);
+}
+
+DocumentMarker* DocumentMarker::cloneWithNewOffsets(unsigned startOffset,
+                                                    unsigned endOffset) const {
+  DocumentMarker* clonedMarker = clone();
+  clonedMarker->setStartOffset(startOffset);
+  clonedMarker->setEndOffset(endOffset);
+
+  return clonedMarker;
+}
+
 DocumentMarker::DocumentMarker(MarkerType type,
                                unsigned startOffset,
                                unsigned endOffset,