Mark test as slow.

tests/lib/lib.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.
 
 [ $compiler == dart2js ]
 math/*: Skip
 mirrors/method_mirror_name_test: Fail # Issue 6335
 mirrors/method_mirror_properties_test: Fail # Issue 11861
 mirrors/method_mirror_returntype_test : Fail # Issue 11928
 mirrors/mirrors_test: Fail # TODO(ahe): I'm working on fixing this.
@@ skipping 51 matching lines @@
 typed_data/float32x4_unbox_phi_test: Fail       # Issue 10961
 typed_data/float32x4_unbox_regress_test: Fail   # Issue 10961
 typed_data/float32x4_shuffle_test: Fail         # Issue 10961
 typed_data/float32x4_two_arg_shuffle_test: Fail # Issue 10961
 
 [ $runtime == ff ]
 # FF setTimeout can fire early: https://bugzilla.mozilla.org/show_bug.cgi?id=291386
 multiple_timer_test: Pass, Fail
 timer_isolate_test: Pass, Fail
 timer_test: Pass, Fail
+convert/chunked_conversion_utf88_test: Pass, Slow  # Issue 12029
 
 [ $runtime == ie9 ]
 # IE9 doesn't support typed arrays.
 typed_data/*: Fail # Issue 11971
+convert/chunked_conversion_utf88_test: Pass, Slow  # Issue 12029
 
 [ $runtime == opera ]
 async/multiple_timer_test: Pass, Fail
 
 [ $runtime == opera && $system == windows]
 # TODO(efortuna): Investigate.
 async/timer_test: Fail, Pass
 
 [ $runtime == vm ]
 async/timer_not_available_test: Fail, OK # only meant to test when there is no way to
@@ skipping 22 matching lines @@
 [ $arch == mips ]
 *: Skip
 
 [ $arch == simmips ]
 typed_data/float32x4_unbox_regress_test: Crash # Unimplemented
 typed_data/float32x4_unbox_phi_test: Crash # Unimplemented
 typed_data/float32x4_list_test: Crash # Unimplemented
 typed_data/float32x4_test: Crash # Unimplemented
 typed_data/float32x4_shuffle_test: Crash # Unimplemented
 typed_data/float32x4_two_arg_shuffle_test: Crash # Unimplemented
+convert/chunked_conversion_utf88_test: Pass, Slow # Issue 12025.