Add option --dump-render-tree to content_shell to dump the render tree as text.

content/shell/shell_render_view_observer.h

 // Copyright (c) 2012 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 CONTENT_SHELL_SHELL_RENDER_VIEW_OBSERVER_H_
 #define CONTENT_SHELL_SHELL_RENDER_VIEW_OBSERVER_H_
 #pragma once
 
 #include "content/public/renderer/render_view_observer.h"
 
 namespace content {
 
 // This class holds the content_shell specific parts of RenderView, and has the
 // same lifetime.
 class ShellRenderViewObserver : public RenderViewObserver {
  public:
   explicit ShellRenderViewObserver(RenderView* render_view);
   virtual ~ShellRenderViewObserver();
 
   // RenderViewObserver implementation.
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
  private:
+  // Message handlers.
+  void OnCaptureTextDump(bool recursive);
+
   DISALLOW_COPY_AND_ASSIGN(ShellRenderViewObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_SHELL_RENDER_VIEW_OBSERVER_H_