Revert of Server push cancellation: add a finch trial parameter

net/http/http_network_session.cc

Index: net/http/http_network_session.cc
diff --git a/net/http/http_network_session.cc b/net/http/http_network_session.cc
index cd58bb6038aef233339a964c68a9ca6d67cc7731..b57653a3b77aea99af3d6904e8f0ee6f2e0a37fd 100644
--- a/net/http/http_network_session.cc
+++ b/net/http/http_network_session.cc
@@ -105,7 +105,6 @@
     : 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),
@@ -399,9 +398,7 @@
 
 void HttpNetworkSession::SetServerPushDelegate(
     std::unique_ptr<ServerPushDelegate> push_delegate) {
-  DCHECK(push_delegate);
-  if (!params_.enable_server_push_cancellation || push_delegate_)
-    return;
+  DCHECK(!push_delegate_ && push_delegate);
 
   push_delegate_ = std::move(push_delegate);
   spdy_session_pool_.set_server_push_delegate(push_delegate_.get());