Marks spawn_shutdown_test Pass, Slow for debug builds.

runtime/tests/vm/vm.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.
 
 # These tests are expected to crash on all platforms.
 cc/ArrayNew_Overflow_Crash: Crash, Timeout
 cc/AllocGeneric_Overflow: Crash, Timeout
 cc/CodeImmutability: Crash
 
 cc/SNPrint_BadArgs: Skip
 
 # Flaky on buildbot. Issue 5133 and 10409.
 cc/Sleep: Pass, Fail
 
 dart/data_uri_import_test/none: SkipByDesign
 
 [ $mode == debug ]
 # This is a benchmark that is not informative in debug mode.
 cc/CorelibIsolateStartup: Skip
 # Negative tests of VerifiedMemory should crash iff in DEBUG mode.
 # TODO(koda): Improve support for negative tests.
 cc/VerifyImplicit_Crash: Crash, Timeout  # Timeout: Issue #24596
 cc/VerifyExplicit_Crash: Crash, Timeout  # Timeout: Issue #24596
+# It can take some time for all the isolates to shutdown in a Debug build.
+dart/spawn_shutdown_test: Pass, Slow  # VM Shutdown test
 
 # The following section refers to the dart vm tests which live under
 # runtime/tests/vm/dart.
 [ $system == windows ]
 cc/Dart2JSCompileAll: Skip
 cc/ExternalizeConstantStrings: Skip
 cc/Service_Profile: Skip
 cc/Dart2JSCompilerStats: Skip
 cc/CorelibCompilerStats: Skip
 
@@ skipping 50 matching lines @@
 [ $noopt ]
 dart/byte_array_test: Crash # Incompatible flag --disable_alloc_stubs_after_gc
 
 [ $noopt || $compiler == precompiler ]
 dart/redirection_type_shuffling_test: CompileTimeError # Imports dart:mirrors
 dart/optimized_stacktrace_test: RuntimeError # Expects line and column numbers
 
 [ $runtime == dart_precompiled ]
 dart/inline_stack_frame_test: Fail  # Issue 24783 - inlined frames missing
 dart/data_uri_spawn_test: RuntimeError # Isolate.spawnUri