Support Document constructor.

third_party/WebKit/Source/core/dom/Document.h

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index 0f79aedd84747debbd272ade4b870f59ec6b91a2..ad3b9481ef8f4f5aee62a56a2042eb7de7b8dd22 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -261,6 +261,11 @@ class CORE_EXPORT Document : public ContainerNode,
   static Document* Create(const DocumentInit& initializer = DocumentInit()) {
     return new Document(initializer);
   }
+  // Factory for web-exposed Document constructor. The argument document must be
+  // a document instance representing window.document, and it works as the
+  // source of ExecutionContext and security origin of the new document.
+  // https://dom.spec.whatwg.org/#dom-document-document
+  static Document* Create(const Document&);
   ~Document() override;
 
   MediaQueryMatcher& GetMediaQueryMatcher();