Set SSLConfig.channel_id_enabled for the proxy config

Prior to crrev.com/c/1026630, SSLConfig.channel_id_enabled defaulted to
true, meaning that the proxy SSLConfig had Channel ID enabled. That CL
flipped SSLConfig.channel_id_enabled to default to false, but only set
channel_id_enabled on the server config, not also the proxy config. This
change should restore the behavior of Channel ID on proxies to what it
was before crrev.com/c/1026630.

Bug: 848953
Change-Id: Ibfde08309803e4bebac622b0d6366a2256ff2b58
Reviewed-on: https://chromium-review.googlesource.com/1089859Reviewed-by: Steven Valdez <svaldez@chromium.org>
Commit-Queue: Nick Harper <nharper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565462}

net/http/http_network_session.cc

@@ -455,6 +455,7 @@ void HttpNetworkSession::GetSSLConfig(const HttpRequestInfo& request,
     server_config->channel_id_enabled = false;
   } else {
     server_config->channel_id_enabled = params_.enable_channel_id;
+    proxy_config->channel_id_enabled = params_.enable_channel_id;
     if (params_.enable_token_binding && context_.channel_id_service) {
       server_config->token_binding_params.push_back(TB_PARAM_ECDSAP256);
     }