Only mark a proxy as bad if we have confirmation that another proxy succeeded for the same request.

net/proxy/proxy_list.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_PROXY_PROXY_LIST_H_
 #define NET_PROXY_PROXY_LIST_H_
 #pragma once
 
 #include <string>
 #include <vector>
 
 #include "net/base/net_export.h"
+#include "net/base/net_log.h"
 #include "net/proxy/proxy_retry_info.h"
 
 namespace net {
 
 class ProxyServer;
 
 // This class is used to hold a list of proxies returned by GetProxyForUrl or
 // manually configured. It handles proxy fallback if multiple servers are
 // specified.
 class NET_EXPORT_PRIVATE ProxyList {
@@ skipping 31 matching lines @@
   // Does a best-effort parse, and silently discards any errors.
   void SetFromPacString(const std::string& pac_string);
 
   // Returns a PAC-style semicolon-separated list of valid proxy servers.
   // For example: "PROXY xxx.xxx.xxx.xxx:xx; SOCKS yyy.yyy.yyy:yy".
   std::string ToPacString() const;
 
   // Marks the current proxy server as bad and deletes it from the list.  The
   // list of known bad proxies is given by proxy_retry_info.  Returns true if
   // there is another server available in the list.
-  bool Fallback(ProxyRetryInfoMap* proxy_retry_info);
+  bool Fallback(ProxyRetryInfoMap* proxy_retry_info,
+                const BoundNetLog& net_log);
 
  private:
   // List of proxies.
   std::vector<ProxyServer> proxies_;
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_LIST_H_