Mark completion_test as slow in checked mode.

pkg/pkg.status

 # Copyright (c) 2012, 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.
 
 # Don't run any test-like files that show up in packages directories. It
 # shouldn't be necessary to run "pub install" in these packages, but if you do
 # it shouldn't break the tests.
 */packages/*/*: Skip
 */*/packages/*/*: Skip
 */*/*/packages/*/*: Skip
 */*/*/*/packages/*/*: Skip
 */*/*/*/*/packages/*/*: Skip
 
 # Analyzer2dart is not maintained anymore.
 analyzer2dart/test/*: Skip
 
 [ $compiler == none && ($runtime == drt || $runtime == dartium) ]
 mutation_observer: Skip # Issue 21149
 unittest/*: Skip # Issue 21949
 lookup_map/*: SkipByDesign
 
 [ $runtime == vm && $mode == debug ]
 analysis_server/test/completion_test: Pass, Slow
 
+[ $runtime == vm && $checked ]
+analysis_server/test/completion_test: Pass, Slow
+
 [ $runtime == vm && $system == windows]
 analysis_server/test/analysis/get_errors_test: Skip # runtime error, Issue 22180
 analysis_server/test/integration/analysis/analysis_options_test: RuntimeError # Issue 24796
 analyzer/test/generated/all_the_rest_test: Fail # Issue 21772
 analyzer_cli/test/driver_test: Fail # Issue 25471
 
 [ $compiler == dart2js ]
 analyzer_cli/test/*: SkipByDesign # Only meant to run on vm
 analysis_server/test/*: Skip # Issue 22161
 analysis_server/test/analysis_notification_highlights_test: Pass, Slow # 19756, 21628
@@ skipping 227 matching lines @@
 analyzer/test/src/task/strong/checker_test: Crash # Issue 24485
 analyzer/test/src/task/strong/inferred_type_test: Crash # Issue 24485
 analyzer/test/src/task/strong_mode_test: Crash # Issue 24485
 analyzer/test/src/task/yaml_test: Crash # Issue 24485
 
 [ $noopt || $runtime == dart_precompiled || $runtime == dart_product ]
 *: SkipByDesign # The pkg test framework imports dart:mirrors.
 
 [ $compiler == dart2js && $cps_ir && $checked ]
 *: Skip # `assert` not implemented, about 75% tests crash