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

net/proxy/proxy_info.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_INFO_H_
 #define NET_PROXY_PROXY_INFO_H_
 #pragma once
 
 #include <string>
 
 #include "net/base/net_export.h"
+#include "net/base/net_log.h"
 #include "net/proxy/proxy_config.h"
 #include "net/proxy/proxy_list.h"
 #include "net/proxy/proxy_retry_info.h"
 #include "net/proxy/proxy_server.h"
 
 namespace net {
 
 // This object holds proxy information returned by ResolveProxy.
 class NET_EXPORT ProxyInfo {
  public:
@@ skipping 57 matching lines @@
 
   // Returns the first valid proxy server. is_empty() must be false to be able
   // to call this function.
   const ProxyServer& proxy_server() const { return proxy_list_.Get(); }
 
   // See description in ProxyList::ToPacString().
   std::string ToPacString() const;
 
   // Marks the current proxy as bad. Returns true if there is another proxy
   // available to try in proxy list_.
-  bool Fallback(ProxyRetryInfoMap* proxy_retry_info);
+  bool Fallback(const BoundNetLog& net_log);
 
   // De-prioritizes the proxies that we have cached as not working, by moving
   // them to the end of the proxy list.
   void DeprioritizeBadProxies(const ProxyRetryInfoMap& proxy_retry_info);
 
   // Deletes any entry which doesn't have one of the specified proxy schemes.
   void RemoveProxiesWithoutScheme(int scheme_bit_field);
 
  private:
   friend class ProxyService;
 
+  const ProxyRetryInfoMap& proxy_retry_info() const {
+    return proxy_retry_info_;
+  }
+
   // The ordered list of proxy servers (including DIRECT attempts) remaining to
   // try. If proxy_list_ is empty, then there is nothing left to fall back to.
   ProxyList proxy_list_;
 
+  // List of proxies that have been tried already.
+  ProxyRetryInfoMap proxy_retry_info_;
+
   // This value identifies the proxy config used to initialize this object.
   ProxyConfig::ID config_id_;
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_INFO_H_