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 378 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 (!params_.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