Enable NetProxyPreconnects experiment by default

net/spdy/chromium/spdy_test_util_common.h

 // Copyright (c) 2013 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_SPDY_SPDY_TEST_UTIL_COMMON_H_
 #define NET_SPDY_SPDY_TEST_UTIL_COMMON_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 198 matching lines @@
   bool enable_user_alternate_protocol_ports;
   bool enable_quic;
   bool enable_server_push_cancellation;
   size_t session_max_recv_window_size;
   SettingsMap http2_settings;
   SpdySession::TimeFunc time_func;
   std::unique_ptr<ProxyDelegate> proxy_delegate;
   bool enable_http2_alternative_service;
   NetLog* net_log;
   bool http_09_on_non_default_ports_enabled;
-  bool restrict_to_one_preconnect_for_proxies;
   bool quic_do_not_mark_as_broken_on_network_change;
 };
 
 class SpdyURLRequestContext : public URLRequestContext {
  public:
   SpdyURLRequestContext();
   ~SpdyURLRequestContext() override;
 
   MockClientSocketFactory& socket_factory() { return socket_factory_; }
 
@@ skipping 308 matching lines @@
 
   GURL default_url_;
 
   // Track a FIFO list of the stream_id of all created requests by priority.
   std::map<int, std::vector<int>> priority_to_stream_id_list_;
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_SPDY_TEST_UTIL_COMMON_H_