Support serializing shadow DOM to MHTML

third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.h

Index: third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.h
diff --git a/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.h b/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.h
index d18c4008649a2d5d4b24f5f10d77c2ecab3983a8..6358aecbc34b7f9ffcf92b9e27734b79d0bd6b7e 100644
--- a/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.h
+++ b/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.h
@@ -75,6 +75,11 @@ class MarkupAccumulator {
 
   EntityMask EntityMaskForText(const Text&) const;
 
+  // Returns the root of auxiliary DOM tree, i.e. shadow tree, if it needs to
+  // be serialized. The additional element to enclose the serialized
+  // auxiliary DOM tree may be returned.
+  virtual Node* GetAuxiliaryDOMTree(const Element&, Element**) const;

[Dmitry Titov, 2017/06/06 04:42:09]

I think it would be clearer to return a std::pair<Node*, Element*>here. 
Also, add comment when each of them can be null.
Also, it'd be good to mention that it creates a new <template> element and
returns it. Maybe change "enclosing element" references to read as "template
element"?

[jianli, 2017/06/07 00:53:42]

Done.

+
  private:
   MarkupFormatter formatter_;
   StringBuilder markup_;