Support Document constructor.

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

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 4c5698d9b2f75ecd9beedc41ca75cfde121445cf..580c36795d7c2b345b9efe3d35d98bfd1f86f0d9 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -491,6 +491,14 @@ class Document::NetworkStateObserver final
   DEFINE_INLINE_VIRTUAL_TRACE() { ContextLifecycleObserver::Trace(visitor); }
 };
 
+Document* Document::Create(const Document& document) {

[dominicc (has gone to gerrit), 2017/05/17 05:50:33]

Could we add a unit test for this? In particular, can you break it when you call
it with different kinds of documents? Where does the application/xml MIME type
come from, for example?

[tkent, 2017/05/17 08:42:18]

Do you mean C++ unit test?
Basically the behavior is web-exposed, and we should have wpt tests instead of
C++ unit test.  Maybe adding wpt/dom/nodes/Document-constructor-svg.svg,
Document-constructor-xml.xml is appropriate.

+  Document* new_document = new Document(
+      DocumentInit::FromContext(const_cast<Document*>(&document), BlankURL()));
+  new_document->SetSecurityOrigin(document.GetSecurityOrigin());
+  new_document->SetContextFeatures(document.GetContextFeatures());
+  return new_document;
+}
+
 Document::Document(const DocumentInit& initializer,
                    DocumentClassFlags document_classes)
     : ContainerNode(0, kCreateDocument),