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

runtime/bin/file_system_watcher_win.cc

 // Copyright (c) 2013, 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.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "bin/file_system_watcher.h"
 #include "bin/eventhandler.h"
 
@@ skipping 55 matching lines @@
   // Issue a read directly, to be sure events are tracked from now on. This is
   // okay, since in Dart, we create the socket and start reading immidiately.
   handle->EnsureInitialized(EventHandler::delegate());
   handle->IssueRead();
   return reinterpret_cast<intptr_t>(handle);
 }
 
 
 void FileSystemWatcher::UnwatchPath(intptr_t id, intptr_t path_id) {
   USE(id);
-  USE(path_id);
+  DirectoryWatchHandle* handle =
+      reinterpret_cast<DirectoryWatchHandle*>(path_id);
+  handle->Stop();
 }
 
 
 intptr_t FileSystemWatcher::GetSocketId(intptr_t id, intptr_t path_id) {
   USE(id);
   return path_id;
 }
 
 
 Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id, intptr_t path_id) {
@@ skipping 31 matching lines @@
     offset += e->NextEntryOffset;
   }
   delete[] buffer;
   return events;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)