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

net/proxy/proxy_info.h

Index: net/proxy/proxy_info.h
diff --git a/net/proxy/proxy_info.h b/net/proxy/proxy_info.h
index f965e6b2eedc7dde423580e2ed47fedc58736e65..2ff8136dc307ee4e36842b4ffbf5d46c813354e8 100644
--- a/net/proxy/proxy_info.h
+++ b/net/proxy/proxy_info.h
@@ -9,6 +9,7 @@
 #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"
@@ -86,7 +87,7 @@ class NET_EXPORT ProxyInfo {
 
   // 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.
@@ -98,10 +99,17 @@ class NET_EXPORT ProxyInfo {
  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_;
 };