socket: Force tunneling for all sockets

In the socket system, only WebSocket sockets are allowed to tunnel
through HTTP/1 proxies. "Raw" sockets in the normal socket pool don't
have it, and their CONNECT headers are not sent, instead the raw
payload is sent as-is to the HTTP/1 proxy, breaking the proxying.

The socket system works like this:

- HTTP sockets via HTTP/1 proxies: normal pool, no tunneling.
- HTTPS sockets via HTTP/1 proxies: normal pool, no tunneling,
  but does its own proxy encapsulation.
- WS sockets via HTTP/1 proxies: WS pool, tunneling.

In Naive, we need the normal pool because the WS pool has some extra
restrictions but we also need tunneling to produce a client socket
with proxy tunneling built in.

Therefore force tunneling for all sockets and have them always send
CONNECT headers. This will otherwise break regular HTTP client sockets
via HTTP/1 proxies, but as we don't use this combination, it is ok.

src/net/socket/client_socket_pool_manager_impl.cc

@@ -86,8 +86,8 @@ ClientSocketPool* ClientSocketPoolManagerImpl::GetSocketPool(
     new_pool = std::make_unique<TransportClientSocketPool>(
         sockets_per_proxy_chain, sockets_per_group,
         unused_idle_socket_timeout(pool_type_), proxy_chain,
-        pool_type_ == HttpNetworkSession::WEBSOCKET_SOCKET_POOL,
-        &common_connect_job_params_, cleanup_on_ip_address_change_);
+        /*force_tunnel=*/true, &common_connect_job_params_,
+        cleanup_on_ip_address_change_);
   }
 
   std::pair<SocketPoolMap::iterator, bool> ret =