Try to remove RuntimeError annotations for mirrors_reader_test.

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.
 
 [ $checked && $compiler != dartanalyzer && $compiler != dart2analyzer && $runtime != dartium ]
 mirrors/regress_16321_test/01: CompileTimeError # Issue 16351
 
 [ $checked && $compiler == none && ($runtime == dartium || $runtime == drt) ]
 mirrors/regress_16321_test/01: RunTimeError # Issue 16351
 
@@ skipping 91 matching lines @@
 mirrors/repeated_private_anon_mixin_app_test: RuntimeError # Issue 14670
 mirrors/symbol_validation_test/01: RuntimeError # Issue 13597
 mirrors/static_members_test: RuntimeError # Issue 14633, Issue 12164
 mirrors/typedef_test/none: RuntimeError # http://dartbug.com/6490
 mirrors/typedef_metadata_test: RuntimeError # Issue 12785
 mirrors/typevariable_mirror_metadata_test: CompileTimeError # Issue 10905
 mirrors/type_variable_is_static_test: RuntimeError # Issue 6335
 mirrors/type_variable_owner_test/01: RuntimeError # Issue 12785
 mirrors/variable_is_const_test/none: RuntimeError # Issue 14671
 mirrors/raw_type_test/01: RuntimeError # http://dartbug.com/6490
-mirrors/mirrors_reader_test: Slow, RuntimeError # Issue 16589
+mirrors/mirrors_reader_test: Slow # Issue 20806
 
 [ $runtime == safari || $runtime == safarimobilesim ]
 typed_data/setRange_2_test: Fail # Safari doesn't fully implement spec for TypedArray.set
 typed_data/setRange_3_test: Fail # Safari doesn't fully implement spec for TypedArray.set
 typed_data/setRange_4_test: Fail # Safari doesn't fully implement spec for TypedArray.set
 typed_data/int32x4_test: Fail, Pass # Safari has an optimization bug (nightlies are already fine).
 typed_data/float32x4_test: Fail, Pass # Safari has an optimization bug (nightlies are already fine).
 mirrors/null_test: Fail # http://dartbug.com/16831
 convert/json_test: Fail # https://bugs.webkit.org/show_bug.cgi?id=134920
 
@@ skipping 81 matching lines @@
 convert/json_lib_test: Fail # Issue 10961
 
 [ $compiler == dart2js && $minified ]
 mirrors/mirrors_used_get_name_test: RuntimeError
 mirrors/mirrors_used_get_name2_test: RuntimeError
 
 [ $runtime == ff ]
 # FF setTimeout can fire early: https://bugzilla.mozilla.org/show_bug.cgi?id=291386
 convert/streamed_conversion_utf8_decode_test: Pass, Slow  # Issue 12029
 convert/streamed_conversion_utf8_encode_test: Pass, Slow # Issue 12029
-mirrors/mirrors_reader_test: Timeout, Slow, RuntimeError # Issue 16589
+mirrors/mirrors_reader_test: Timeout, Slow # Issue 20806
 
 [ $runtime == ie9 ]
 # IE9 doesn't support typed arrays.
 typed_data/*: Fail # Issue 11971
 convert/chunked_conversion_utf88_test: Skip  # Issue 12029
 convert/streamed_conversion_json_utf8_decode_test: Skip # Issue 12029
 async/deferred/*: Skip # http://dartbug.com/12635
 mirrors/deferred*: Pass, Fail # http://dartbug.com/12635
 convert/streamed_conversion_utf8_decode_test: Skip # http://dartbug.com/12768
 convert/utf85_test: Skip # Issue 12029.
 convert/json_util_test: Fail # Issue 16109
-mirrors/mirrors_reader_test: Slow, RuntimeError # Issue 16589
+mirrors/mirrors_reader_test: Slow # Issue 20806
 
 [ $compiler == dart2js ]
 typed_data/typed_data_hierarchy_int64_test: RuntimeError # Issue 10275
 typed_data/int32x4_bigint_test: RuntimeError # Issue 1533
 
 [ $runtime == opera ]
 async/multiple_timer_test: Pass, Fail # Probably issue 14734
 
 [ $runtime == opera && $system == windows]
 # TODO(efortuna): Investigate.
@@ skipping 88 matching lines @@
 
 [ $arch == simarm ]
 convert/chunked_conversion_utf88_test: Skip  # Pass, Slow Issue 12644.
 convert/utf85_test: Skip  # Pass, Slow Issue 12644.
 
 [ $compiler == dart2js ]
 profiler/metrics_num_test: Skip # Because of a int / double type test.
 
 [ $arch == simarm64 ]
 convert/utf85_test: Skip # Pass, Slow Issue 20111.