Enable NetProxyPreconnects experiment by default

net/http/http_network_session.h

 // Copyright (c) 2012 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_HTTP_HTTP_NETWORK_SESSION_H_
 #define NET_HTTP_HTTP_NETWORK_SESSION_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 170 matching lines @@
     // If true, estimate the initial RTT for QUIC connections based on network.
     bool quic_estimate_initial_rtt;
 
     ProxyDelegate* proxy_delegate;
     // Enable support for Token Binding.
     bool enable_token_binding;
 
     // Enable HTTP/0.9 for HTTP/HTTPS on ports other than the default one for
     // each protocol.
     bool http_09_on_non_default_ports_enabled;
-
-    // If true, only one pending preconnect is allowed to proxies that support
-    // request priorities.
-    bool restrict_to_one_preconnect_for_proxies;
   };
 
   enum SocketPoolType {
     NORMAL_SOCKET_POOL,
     WEBSOCKET_SOCKET_POOL,
     NUM_SOCKET_POOL_TYPES
   };
 
   explicit HttpNetworkSession(const Params& params);
   ~HttpNetworkSession() override;
@@ skipping 121 matching lines @@
   NextProtoVector next_protos_;
 
   Params params_;
 
   std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_NETWORK_SESSION_H_