Update status of flaky windows vm tests

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.
 
 [ $unchecked ]
 mirrors/redirecting_factory_different_type_test: SkipByDesign # Tests type checks.
 
 [ $compiler == dart2js ]
 async/schedule_microtask6_test: RuntimeError # global error handling is not supported. Issue 5958
 
@@ skipping 301 matching lines @@
 
 [ $compiler == dart2js ]
 developer/metrics_num_test: Skip # Because of a int / double type test.
 
 [ $arch == simarm64 ]
 convert/utf85_test: Skip # Pass, Slow Issue 20111.
 
 [ $mode == debug && $arch == ia32 && $system == windows ]
 convert/streamed_conversion_json_utf8_decode_test: Skip  # Verification OOM.
 
+[ $runtime == vm && $mode == debug && $arch == x64 && $system == windows ]
+convert/streamed_conversion_json_utf8_decode_test: Pass, Slow
+
 [ $mode == debug && $arch != ia32 && $arch != x64 && $arch != simarm && $arch != simarmv5te ]
 convert/streamed_conversion_json_utf8_decode_test: Skip  # Verification not yet implemented.
 
 [ $runtime == vm && $mode == debug && $builder_tag == asan ]
 mirrors/immutable_collections_test: SkipSlow  # Timeout.
 convert/streamed_conversion_json_utf8_decode_test: Skip  # Timeout.
 
 [ $compiler == dart2js && $cps_ir ]
 async/future_test/01: Crash # (()async=>new Future.value(value)): cannot handle async/sync*/async* functions
 async/stream_empty_test: Crash # (Future runTest()asy...  cannot handle async/sync*/async* functions
 async/stream_iterator_test: Crash # (()async{var stream=...  cannot handle async/sync*/async* functions
 convert/ascii_test: RuntimeError # this.get$length is not a function
 convert/latin1_test: RuntimeError # this.get$length is not a function
 mirrors/deferred_mirrors_metadata_test: RuntimeError # U.loadLibrary is not a function
 mirrors/deferred_mirrors_metatarget_test: RuntimeError # X.loadLibrary is not a function
 mirrors/deferred_mirrors_update_test: RuntimeError # U.loadLibrary is not a function
 mirrors/delegate_call_through_getter_test: RuntimeError # Please triage this failure.
 mirrors/delegate_test: RuntimeError # Please triage this failure.
 mirrors/library_enumeration_deferred_loading_test: RuntimeError # L.loadLibrary is not a function
 mirrors/symbol_validation_test/none: RuntimeError # Please triage this failure.
 mirrors/typedef_deferred_library_test: RuntimeError # G.loadLibrary is not a function
 typed_data/typed_data_list_test: RuntimeError # this.get$length is not a function