Makes a handful of DataSources not replace the existing

chrome/browser/dom_ui/web_ui_theme_source.h

 // Copyright (c) 2011 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 CHROME_BROWSER_DOM_UI_WEB_UI_THEME_SOURCE_H_
 #define CHROME_BROWSER_DOM_UI_WEB_UI_THEME_SOURCE_H_
 #pragma once
 
 #include <string>
 
 #include "chrome/browser/webui/chrome_url_data_manager.h"
 
 class Profile;
 class RefCountedBytes;
 
 class WebUIThemeSource : public ChromeURLDataManager::DataSource {
  public:
   explicit WebUIThemeSource(Profile* profile);
 
   // Called when the network layer has requested a resource underneath
   // the path we registered.
   virtual void StartDataRequest(const std::string& path,
                                 bool is_off_the_record,
                                 int request_id);
   virtual std::string GetMimeType(const std::string& path) const;
 
   // Used to tell ChromeURLDataManager which thread to handle the request on.
   virtual MessageLoop* MessageLoopForRequestPath(const std::string& path) const;
 
+  virtual bool ShouldReplaceExistingSource() const;
+
  protected:
   virtual ~WebUIThemeSource();
 
  private:
   // Fetch and send the theme bitmap.
   void SendThemeBitmap(int request_id, int resource_id);
 
   // The original profile (never an OTR profile).
   Profile* profile_;
 
   // We grab the CSS early so we don't have to go back to the UI thread later.
   scoped_refptr<RefCountedBytes> css_bytes_;
 
   DISALLOW_COPY_AND_ASSIGN(WebUIThemeSource);
 };
 
 #endif  // CHROME_BROWSER_DOM_UI_WEB_UI_THEME_SOURCE_H_