Remove dead markup serialization code.

sky/viewer/internals.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKY_VIEWER_INTERNALS_H_
 #define SKY_VIEWER_INTERNALS_H_
 
 #include "base/memory/weak_ptr.h"
 #include "gin/handle.h"
 #include "gin/object_template_builder.h"
@@ skipping 11 matching lines @@
   virtual ~Internals();
 
   virtual gin::ObjectTemplateBuilder GetObjectTemplateBuilder(
       v8::Isolate* isolate) override;
 
  private:
   explicit Internals(DocumentView* document_view);
 
   std::string RenderTreeAsText();
   std::string ContentAsText();
-  std::string ContentAsMarkup();
   void NotifyTestComplete(const std::string& test_result);
 
   mojo::Handle ConnectToService(
       const std::string& application_url, const std::string& interface_name);
 
   base::WeakPtr<DocumentView> document_view_;
   TestHarnessPtr test_harness_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(Internals);
 };
 
 }  // namespace sky
 
 #endif  // SKY_VIEWER_INTERNALS_H_