Add DocumentMarker::clone()

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

Index: third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.cpp
diff --git a/third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.cpp b/third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..fd9f026d32ca07e40ca825ed206227cc8c409f89
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/markers/RenderedDocumentMarker.cpp
@@ -0,0 +1,13 @@
+// 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.
+
+#include "core/editing/markers/RenderedDocumentMarker.h"
+
+namespace blink {
+
+RenderedDocumentMarker* RenderedDocumentMarker::clone() const {
+  return new RenderedDocumentMarker(*this);
+}
+
+}  // namespace blink