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

net/base/net_log_event_type_list.h

Index: net/base/net_log_event_type_list.h
diff --git a/net/base/net_log_event_type_list.h b/net/base/net_log_event_type_list.h
index c0ebe19cec54ba504604b6f14a50b43b2cdcb793..db26071c5719441b1d2481acdfdad24ad82401b0 100644
--- a/net/base/net_log_event_type_list.h
+++ b/net/base/net_log_event_type_list.h
@@ -220,6 +220,28 @@ EVENT_TYPE(PROXY_SERVICE_RESOLVED_PROXY_LIST)
 // proxy settings (since there wasn't a previous value).
 EVENT_TYPE(PROXY_CONFIG_CHANGED)
 
+// Emitted when a list of bad proxies is reported to the proxy service.
+//
+// Parameters:
+//   {
+//     "bad_proxy_list": <List of bad proxies>,
+//   }
+EVENT_TYPE(BAD_PROXY_LIST_REPORTED)
+
+// ------------------------------------------------------------------------
+// ProxyList
+// ------------------------------------------------------------------------
+
+// Emitted when the first proxy server in a list is being marked as
+// bad and proxy resolution is going to failover to the next one in
+// the list.  The fallback is local to the request.
+//
+// Parameters:
+//   {
+//     "bad_proxy": <URI representation of the failed proxy server>,
+//   }
+EVENT_TYPE(PROXY_LIST_FALLBACK)
+
 // ------------------------------------------------------------------------
 // Proxy Resolver
 // ------------------------------------------------------------------------