Enable NetProxyPreconnects experiment by default

net/http/http_stream_factory_impl.cc

 // 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.
 
 #include "net/http/http_stream_factory_impl.h"
 
 #include <string>
 #include <tuple>
 
 #include "base/logging.h"
@@ skipping 282 matching lines @@
 }
 
 bool HttpStreamFactoryImpl::OnInitConnection(const JobController& controller,
                                              const ProxyInfo& proxy_info,
                                              PrivacyMode privacy_mode) {
   if (!controller.is_preconnect()) {
     // Connection initialization can be skipped only for the preconnect jobs.
     return false;
   }
 
-  if (!session_->params().restrict_to_one_preconnect_for_proxies ||
-      !ProxyServerSupportsPriorities(proxy_info)) {
+  if (!ProxyServerSupportsPriorities(proxy_info))
     return false;
-  }
 
   PreconnectingProxyServer preconnecting_proxy_server(proxy_info.proxy_server(),
                                                       privacy_mode);
 
   if (base::ContainsKey(preconnecting_proxy_servers_,
                         preconnecting_proxy_server)) {
     UMA_HISTOGRAM_EXACT_LINEAR("Net.PreconnectSkippedToProxyServers", 1, 2);
     // Skip preconnect to the proxy server since we are already preconnecting
     // (probably via some other job).

[xunjieli, 2017/04/28 14:24:31]

Could you link crbug.com/682041 in this comment?

[tbansal1, 2017/04/28 16:36:08]

Done.

     return true;
   }
 
   // Add the proxy server to the set of preconnecting proxy servers.
   // The maximum size of |preconnecting_proxy_servers_|.
   static const size_t kMaxPreconnectingServerSize = 3;
   if (preconnecting_proxy_servers_.size() >= kMaxPreconnectingServerSize) {
     // Erase the first entry. A better approach (at the cost of higher memory
     // overhead) may be to erase the least recently used entry.
     preconnecting_proxy_servers_.erase(preconnecting_proxy_servers_.begin());
@@ skipping 126 matching lines @@
   factory_dump->AddScalar("main_job_count",
                           base::trace_event::MemoryAllocatorDump::kUnitsObjects,
                           main_job_count);
   // The number of preconnect controllers.
   factory_dump->AddScalar("preconnect_count",
                           base::trace_event::MemoryAllocatorDump::kUnitsObjects,
                           num_controllers_for_preconnect);
 }
 
 }  // namespace net