Mark pkg/crypto/test/hmac_sha256_test as flaky

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
@@ skipping 44 matching lines @@
 intl/test/date_time_format_http_request_test: Fail # Issue 8983
 mime/test/mime_multipart_transformer_test: Skip # No typed_data on IE9.
 sequence_zip/test/stream_test: Pass, Fail # Flaky, issue 12873
 
 [ $runtime == safari ]
 fixnum/test/int_64_test: Pass, Fail # Bug in JSC.
 crypto/test/hmac_sha1_test: Pass, Fail # Issue 11407.
 crypto/test/sha1_test: Fail # Issue 11407.
 stack_trace/test/trace_test: Fail # http://dartbug.com/12380
 crypto/test/sha256_test: Pass, Fail # Issue 12502
+crypto/test/hmac_sha256_test: Pass, Fail # Issue 12502
 
 # Skip browser-specific tests on VM
 [ $runtime == vm ]
 path/test/browser_test: Fail, OK # Uses dart:html
 intl/test/find_default_locale_browser_test: Skip
 intl/test/date_time_format_http_request_test: Skip
 
 [ $runtime == vm && $system == windows ]
 docgen/test/single_library_test: Fail # Issue 11985
 intl/test/find_default_locale_standalone_test: Fail # Issue 8110
@@ skipping 130 matching lines @@
 
 [ $browser || $runtime == vm ]
 unittest/test/missing_tick_test: Fail, OK # This test should fail, not time out.
 
 # Issue http://dartbug.com/12930
 [ $runtime == vm ]
 intl/test/message_extraction/message_extraction_test: Pass, Fail # Issue 12930
 
 [ $compiler == none && $runtime == drt && $arch == ia32 ]
 custom_element/test/custom_element_test: Fail, Pass # http://dartbug.com/12964