Warn when adding something to a closed sink and improve documentation

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.
 
 # WARNING:
 # Tests using the multitest feature where failure is expected should *also* be
 # listed in tests/lib/analyzer/analyze_tests.status without the "standalone"
 # prefix.
 
 io/raw_socket_test: Pass, RuntimeError # Issue 28288
@@ skipping 85 matching lines @@
 
 [ $compiler == dartanalyzer || $compiler == dart2analyzer ]
 issue14236_test: Skip # Analyzer can't handle Script snapshots.
 
 # test issue https://code.google.com/p/dart/issues/detail?id=11518
 io/file_constructor_test: fail
 
 # This is runtime test.
 io/process_exit_negative_test: Skip
 
-io/http_parser_test: Pass, CompileTimeError # Issue 28843
-io/http_headers_test: Pass, CompileTimeError # Issue 28843
-io/http_cookie_date_test: Pass, CompileTimeError # Issue 28843
-io/web_socket_protocol_processor_test: Pass, CompileTimeError # Issue 28843
+io/http_parser_test: Pass, StaticWarning, CompileTimeError # Issue 28843
+io/http_headers_test: Pass, StaticWarning, CompileTimeError # Issue 28843
+io/http_cookie_date_test: Pass, StaticWarning, CompileTimeError # Issue 28843
+io/web_socket_protocol_processor_test: Pass, StaticWarning, CompileTimeError # Issue 28843
 
 [ $compiler == dart2analyzer && $builder_tag == strong ]
 *: Skip # Issue 28649
 
 [ $compiler == dart2js ]
 regress_29350_test: MissingCompileTimeError
 number_identity_test: Skip # Bigints and int/double diff. not supported.
 typed_data_test: Skip # dart:typed_data support needed.
 bytedata_test: Skip # dart:typed_data support needed.
 typed_data_view_test: Skip # dart:typed_data support needed.
@@ skipping 418 matching lines @@
 package/scenarios/packages_dir_only/packages_dir_only_test: Fail # Unable to parse package files Flutter Issue 9115
 package/scenarios/both_dir_and_file/prefers_packages_file_test: Fail # Unable to parse package files Flutter Issue 9115
 package/package_test: Fail # Unable to parse package files Flutter Issue 9115
 #unboxed_int_converter_test: Fail # Unable to parse package files Flutter Issue 9115
 io/process_run_output_test: Fail # Unable to parse package files Flutter Issue 9115
 
 io/test_harness_analyzer_test: CompileTimeError # Uses mirrors
 io/skipping_dart2js_compilations_test: CompileTimeError # Uses mirrors
 io/test_runner_test: CompileTimeError # Uses mirrors