Re-implement directory polling.

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
 
 # Skip non-test files ending with "_test".
 scheduled_test/lib/*: Skip
 
 scheduled_test/test/scheduled_server_test: Pass, Fail, Slow, Crash # Issue 9231, 9582
 scheduled_test/test/scheduled_process_test: Pass, Slow # Issue 9231
 
-[ $runtime == vm ]
-watcher/test/no_subscription_test: Pass, Fail # Issue 12107
-watcher/test/directory_watcher_test: Pass, Fail # Issue 12107
-
 [ $runtime == d8 || $runtime == jsshell ]
 unittest/test/unittest_nested_groups_setup_teardown_test: Pass, Fail # http://dartbug.com/10109
 stack_trace/test/vm_test: Fail, OK # VM-specific traces
 sequence_zip/test/stream_test: Fail, OK # Timers are not supported.
 
 [$compiler == dart2dart]
 *: Skip
 
 [ $compiler == dart2js || $compiler == dart2dart ]
 source_maps/test/vlq_test: Fail # A VLQ test checks for large numbers that
@@ skipping 140 matching lines @@
 
 # Skip tests on the VM if the package depends on dart:html
 [ $runtime == vm ]
 custom_element: Skip
 mdv: Skip
 mutation_observer: Skip
 
 [ $runtime == safari || $runtime == chrome || $runtime == ie9 || $runtime == ff || $runtime == dartium || $runtime == drt ]
 docgen/test/single_library_test: Skip # Uses dart:io