Add some more headless API feature placeholders

headless/public/web_frame.h

 // Copyright 2015 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 HEADLESS_PUBLIC_WEB_FRAME_H_
 #define HEADLESS_PUBLIC_WEB_FRAME_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/values.h"
@@ skipping 26 matching lines @@
   //    will return [1, 2, 3]).
   // - Object will be converted to base::DictionaryValue
   //   Note: Only string can be key in base::DictionaryValue, so all non-string
   //   properties will be omitted
   //   (e.g. "obj = Object(); obj['key'] = 'value'; obj[0] = 42;" will return
   //    {"key":"value"}).
   virtual void ExecuteScriptAndReturnValue(
       const std::string& source_code,
       const ScriptExecutionCallback& callback) = 0;
 
+  virtual std::string ContentAsText(size_t max_chars) const = 0;
+  virtual std::string ContentAsMarkup() const = 0;
+  virtual proto::Document ContentAsProtobuf() const = 0;
+
+  virtual gfx::Size GetScrollOffset() const = 0;
+  virtual void SetScrollOffset(const gfx::Size& offset) = 0;
+
+  virtual float GetPageScaleFactor() const = 0;
+  virtual void SetPageScaleFactor(float page_scale_factor) = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(WebFrame);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_WEB_FRAME_H_