Server push cancellation: add a finch trial parameter

net/http/http_network_session.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_network_session.h"
 
 #include <utility>
 
 #include "base/atomic_sequence_num.h"
 #include "base/compiler_specific.h"
@@ skipping 85 matching lines @@
 
   return http2_settings;
 }
 
 }  // unnamed namespace
 
 HttpNetworkSession::Params::Params()
     : client_socket_factory(nullptr),
       host_resolver(nullptr),
       cert_verifier(nullptr),
+      enable_server_push_cancellation(false),
       channel_id_service(nullptr),
       transport_security_state(nullptr),
       cert_transparency_verifier(nullptr),
       ct_policy_enforcer(nullptr),
       proxy_service(nullptr),
       ssl_config_service(nullptr),
       http_auth_handler_factory(nullptr),
       net_log(nullptr),
       host_mapping_rules(nullptr),
       socket_performance_watcher_factory(nullptr),
@@ skipping 49 matching lines @@
 
 HttpNetworkSession::Params::Params(const Params& other) = default;
 
 HttpNetworkSession::Params::~Params() {}
 
 // TODO(mbelshe): Move the socket factories into HttpStreamFactory.
 HttpNetworkSession::HttpNetworkSession(const Params& params)
     : net_log_(params.net_log),
       http_server_properties_(params.http_server_properties),
       cert_verifier_(params.cert_verifier),
+      enable_server_push_cancellation_(params.enable_server_push_cancellation),
       http_auth_handler_factory_(params.http_auth_handler_factory),
       proxy_service_(params.proxy_service),
       ssl_config_service_(params.ssl_config_service),
       push_delegate_(nullptr),
       quic_stream_factory_(
           params.net_log,
           params.host_resolver,
           params.ssl_config_service,
           params.client_socket_factory
               ? params.client_socket_factory
@@ skipping 204 matching lines @@
       return params_.enable_http2;
     case kProtoQUIC:
       return IsQuicEnabled();
   }
   NOTREACHED();
   return false;
 }
 
 void HttpNetworkSession::SetServerPushDelegate(
     std::unique_ptr<ServerPushDelegate> push_delegate) {
-  DCHECK(!push_delegate_ && push_delegate);
+  DCHECK(push_delegate);
+  if (!enable_server_push_cancellation_ || push_delegate_)
+    return;
 
   push_delegate_ = std::move(push_delegate);
   spdy_session_pool_.set_server_push_delegate(push_delegate_.get());
   quic_stream_factory_.set_server_push_delegate(push_delegate_.get());
 }
 
 void HttpNetworkSession::GetAlpnProtos(NextProtoVector* alpn_protos) const {
   *alpn_protos = next_protos_;
 }
 
@@ skipping 70 matching lines @@
       CloseIdleConnections();
       break;
   }
 }
 
 void HttpNetworkSession::OnPurgeMemory() {
   CloseIdleConnections();
 }
 
 }  // namespace net