Gardening: Mark io/http_basic_test slow. Add debug prints into io/process_start_exception_test.

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 45 matching lines @@
 # This test sometimes hangs on Mac.
 io/raw_server_socket_cancel_test: Skip # Issue 28182
 
 [ $runtime == vm && $system == linux ]
 # These tests have started timing out and issue 25649 has been filed to
 # investigate, skipping these tests temporarily to get the bots to be
 # green again.
 io/http_proxy_test: Skip
 io/secure_builtin_roots_test: Skip
 
+# This test might be slow on an opt counter threshold bot.
+io/http_basic_test: Pass, Slow
+
 
 [ $compiler == none && ($runtime == drt || $runtime == dartium) ]
 typed_array_test: RuntimeError, OK  # Uses Isolate.spawn
 typed_array_int64_uint64_test: RuntimeError, OK  # Uses Isolate.spawn
 typed_data_isolate_test: SkipByDesign # This test uses dart:io
 io/*: SkipByDesign # Don't run tests using dart:io in the browser
 package/*: Skip # Do not run those in Dartium.
 http_launch_test: Skip
 vmservice/*: SkipByDesign # Do not run standalone vm service tests in browser.
 issue14236_test: Skip # Issue 14236 Script snapshots do not work in the browser.
@@ skipping 308 matching lines @@
 io/directory_list_nonexistent_test: Fail # Issue 28350
 
 io/stdout_bad_argument_test: Fail # Issue 28353
 io/file_blocking_lock_test: Fail # Issue 28353
 
 io/process_sync_test: RuntimeError
 io/signals_test: RuntimeError
 io/regress_7191_test: RuntimeError
 io/named_pipe_script_test: RuntimeError
 io/http_server_close_response_after_error_test: RuntimeError