Support serializing shadow DOM to MHTML

third_party/WebKit/Source/core/frame/FrameSerializer.cpp

Index: third_party/WebKit/Source/core/frame/FrameSerializer.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameSerializer.cpp b/third_party/WebKit/Source/core/frame/FrameSerializer.cpp
index a2258654313ad94f65350fda26b7e48f38c62b14..d8d5dbd7c819c7fe2ed92ebd4ed19ff85f179cb3 100644
--- a/third_party/WebKit/Source/core/frame/FrameSerializer.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameSerializer.cpp
@@ -102,6 +102,7 @@ class SerializerMarkupAccumulator : public MarkupAccumulator {
                        Namespaces*) override;
   void AppendStartTag(Node&, Namespaces* = nullptr) override;
   void AppendEndTag(const Element&) override;
+  Node* GetAuxiliaryDOMTree(const Element&, Element**) const override;
 
  private:
   void AppendAttributeValue(StringBuilder& out, const String& attribute_value);
@@ -232,6 +233,12 @@ void SerializerMarkupAccumulator::AppendEndTag(const Element& element) {
   MarkupAccumulator::AppendEndTag(element);
 }
 
+Node* SerializerMarkupAccumulator::GetAuxiliaryDOMTree(
+    const Element& element,
+    Element** enclosing_element) const {
+  return delegate_.GetAuxiliaryDOMTree(element, enclosing_element);
+}
+
 void SerializerMarkupAccumulator::AppendAttributeValue(
     StringBuilder& out,
     const String& attribute_value) {