Use 'Directory.watch' on Windows in pkg/watcher, instead of pooling.

pkg/analysis_server/test/physical_resource_provider_test.dart

Index: pkg/analysis_server/test/physical_resource_provider_test.dart
diff --git a/pkg/analysis_server/test/physical_resource_provider_test.dart b/pkg/analysis_server/test/physical_resource_provider_test.dart
index f2af810a7b48daf3deccc73854daec8b31b764a8..839f1c48dcc4bac672641d572c64e372eadde8eb 100644
--- a/pkg/analysis_server/test/physical_resource_provider_test.dart
+++ b/pkg/analysis_server/test/physical_resource_provider_test.dart
@@ -32,10 +32,7 @@ main() {
       group('Watch', () {
 
         Future delayed(computation()) {
-          // On Windows, watching the filesystem is accomplished by polling once
-          // per second.  So wait 2 seconds to give time for polling to reliably
-          // occur.
-          return new Future.delayed(new Duration(seconds: 2), computation);
+          return new Future.delayed(new Duration(milliseconds: 100), computation);
         }
 
         watchingFolder(String path, test(List<WatchEvent> changesReceived)) {