Allow at most one preconnect to HTTP2 proxy servers

net/http/http_stream_factory_impl_job_controller.h

Index: net/http/http_stream_factory_impl_job_controller.h
diff --git a/net/http/http_stream_factory_impl_job_controller.h b/net/http/http_stream_factory_impl_job_controller.h
index 770071f68b12c382c919473e96c891bca075ad81..c4edf161dbaa0771cc829c3c65c6ced51488f99b 100644
--- a/net/http/http_stream_factory_impl_job_controller.h
+++ b/net/http/http_stream_factory_impl_job_controller.h
@@ -117,6 +117,8 @@ class HttpStreamFactoryImpl::JobController
                         const ProxyInfo& used_proxy_info,
                         HttpAuthController* auth_controller) override;
 
+  bool OnInitConnection(const ProxyInfo& proxy_info) override;
+
   void OnResolveProxyComplete(
       Job* job,
       const HttpRequestInfo& request_info,
@@ -167,6 +169,8 @@ class HttpStreamFactoryImpl::JobController
   WebSocketHandshakeStreamBase::CreateHelper*
   websocket_handshake_stream_create_helper() override;
 
+  bool is_preconnect() const { return is_preconnect_; }
+
  private:
   friend class JobControllerPeer;