Re-implement http sessions.

tests/standalone/standalone.status

 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Temporary IO library change disables, timeout
 io/http_advanced_test: skip
 io/http_read_test: skip
 
 
 # Temporary IO library change disables, fail
 # HTTP tests
 io/http_connection_header_test: fail
 io/http_connection_info_test: fail
 io/http_content_length_test: fail
 io/http_date_test: fail
 io/http_head_test: fail
 io/http_headers_state_test: fail
 io/http_headers_test: fail
 io/http_parser_test: fail
 io/http_server_early_client_close_test: fail
 io/http_server_early_server_close_test: fail
 io/http_server_handler_test: fail
 io/http_server_socket_test: fail
-io/http_session_test: fail
 io/http_shutdown_test: fail
 io/https_client_certificate_test: fail
 io/https_client_test: fail
 io/https_server_test: fail
 
 # Other
 io/dart_std_io_pipe_test: fail
 io/echo_server_stream_test: fail
 io/echo_server_test: fail
 io/process_stderr_test: fail
@@ skipping 154 matching lines @@
 [ $compiler == dart2js && $browser ]
 *: Skip
 
 [ $compiler == dart2js && $checked ]
 io/http_read_test: Skip # Timeout TODO(ngeoffray): investigate
 io/list_input_stream_test: Skip # Timeout TODO(ngeoffray): investigate
 
 [ $compiler == dart2dart ]
 # Skip until we stabilize language tests.
 *: Skip