Avoid cross-origin iframe issues when loading PDF in print preview

content/public/browser/url_data_source.h

 // Copyright (c) 2013 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_PUBLIC_BROWSER_URL_DATA_SOURCE_H_
 #define CONTENT_PUBLIC_BROWSER_URL_DATA_SOURCE_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 115 matching lines @@
   // |origin|, or "*", or "none", or empty string.
   // Default implementation returns an empty string.
   virtual std::string GetAccessControlAllowOriginForOrigin(
       const std::string& origin) const;
 
   // Called to inform the source that StartDataRequest() will be called soon.
   // Gives the source an opportunity to rewrite |path| to incorporate extra
   // information from the URLRequest prior to serving.
   virtual void WillServiceRequest(
       const net::URLRequest* request,
-      std::string* path) const {}
+      std::string* path) const;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_URL_DATA_SOURCE_H_