Add stack chain support to pkg/watcher and pkg/http.

pkg/watcher/lib/src/directory_watcher/polling.dart

 // 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.
 
 library watcher.directory_watcher.polling;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:crypto/crypto.dart';
+import 'package:stack_trace/stack_trace.dart';
 
 import '../async_queue.dart';
 import '../stat.dart';
 import '../utils.dart';
 import '../watch_event.dart';
 import 'resubscribable.dart';
 
 /// Periodically polls a directory for changes.
 class PollingDirectoryWatcher extends ResubscribableDirectoryWatcher {
   /// Creates a new polling watcher monitoring [directory].
@@ skipping 77 matching lines @@
     _polledFiles.clear();
 
     endListing() {
       assert(!_events.isClosed);
       _listSubscription = null;
 
       // Null tells the queue consumer that we're done listing.
       _filesToProcess.add(null);
     }
 
-    var stream = new Directory(directory).list(recursive: true);
+    var stream = Chain.track(new Directory(directory).list(recursive: true));
     _listSubscription = stream.listen((entity) {
       assert(!_events.isClosed);
 
       if (entity is! File) return;
       _filesToProcess.add(entity.path);
     }, onError: (error, stackTrace) {
       if (!isDirectoryNotFoundException(error)) {
         // It's some unknown error. Pipe it over to the event stream so the
         // user can see it.
         _events.addError(error, stackTrace);
@@ skipping 59 matching lines @@
 
     // Wait and then poll again.
     return new Future.delayed(_pollingDelay).then((_) {
       if (_events.isClosed) return;
       _poll();
     });
   }
 
   /// Calculates the SHA-1 hash of the file at [path].
   Future<List<int>> _hashFile(String path) {
-    return new File(path).readAsBytes().then((bytes) {
+    return Chain.track(new File(path).readAsBytes()).then((bytes) {
       var sha1 = new SHA1();
       sha1.add(bytes);
       return sha1.close();
     });
   }
 
   /// Returns `true` if [a] and [b] are the same hash value, i.e. the same
   /// series of byte values.
   bool _sameHash(List<int> a, List<int> b) {
     // Hashes should always be the same size.
@@ skipping 10 matching lines @@
 class _FileStatus {
   /// The last time the file was modified.
   DateTime modified;
 
   /// The SHA-1 hash of the contents of the file.
   List<int> hash;
 
   _FileStatus(this.modified, this.hash);
 }