Improve merging of header modifications in webRequest.OnHeadersReceived

net/url_request/url_request_http_job.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 NET_URL_REQUEST_URL_REQUEST_HTTP_JOB_H_
 #define NET_URL_REQUEST_URL_REQUEST_HTTP_JOB_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 202 matching lines @@
 
   // The start time for the job, ignoring re-starts.
   base::TimeTicks start_time_;
 
   scoped_ptr<HttpFilterContext> filter_context_;
   ScopedRunnableMethodFactory<URLRequestHttpJob> method_factory_;
   base::WeakPtrFactory<URLRequestHttpJob> weak_ptr_factory_;
 
   OldCompletionCallbackImpl<URLRequestHttpJob> on_headers_received_callback_;
 
+  // We allow the network delegate to modify a copy of the response headers.
+  // This prevents modifications of headers that are shared with the underlying
+  // layers of the network stack.
   scoped_refptr<HttpResponseHeaders> override_response_headers_;
 
   // Flag used to verify that |this| is not deleted while we are awaiting
   // a callback from the NetworkDelegate. Used as a fail-fast mechanism.
   // True if we are waiting a callback and
   // NetworkDelegate::NotifyURLRequestDestroyed has not been called, yet,
   // to inform the NetworkDelegate that it may not call back.
   bool awaiting_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(URLRequestHttpJob);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_HTTP_JOB_H_