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 2b43599d5ec2cdf32815f444145cd0cc924a45a7..272da6656166c969ebc2f8a178339e0e3aa230e7 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;
+  std::pair<Node*, Element*> GetAuxiliaryDOMTree(const Element&) const override;
 
  private:
   void AppendAttributeValue(StringBuilder& out, const String& attribute_value);
@@ -232,6 +233,11 @@ void SerializerMarkupAccumulator::AppendEndTag(const Element& element) {
   MarkupAccumulator::AppendEndTag(element);
 }
 
+std::pair<Node*, Element*> SerializerMarkupAccumulator::GetAuxiliaryDOMTree(
+    const Element& element) const {
+  return delegate_.GetAuxiliaryDOMTree(element);
+}
+
 void SerializerMarkupAccumulator::AppendAttributeValue(
     StringBuilder& out,
     const String& attribute_value) {